Salt, acid generator, resist composition and method for producing resist pattern

ABSTRACT

Described are a salt and a resist composition capable of producing a resist pattern with satisfactory line edge roughness (LER). The salt is represented by formula (I): 
                         
In formula (I), R 1 , R 2 , R 3 , R 4  and R 5  each independently represent a halogen atom or a perfluoroalkyl group having 1 to 6 carbon atoms, R 6 , R 7  and R 8  each independently represent a halogen atom, a hydroxy group, a fluorinated alkyl group having 1 to 6 carbon atoms or an alkyl group having 1 to 12 carbon atoms, and —CH 2 — included in the alkyl group may be replaced by —O— or —CO—, m5 represents an integer of 1 to 5, m6 represents an integer of 0 to 3, m7 represents an integer of 0 to 3, m8 represents an integer of 0 to 4, and AI −  represents an organic anion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2018-077035, filed on Apr. 12, 2018, the entire content of which ishereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a salt for acid generator which is usedfor fine processing of a semiconductor, an acid generator containing thesalt, a resist composition and a method for producing a resist pattern.

BACKGROUND ART

Patent Document 1 mentions a salt represented by the following formula,and a resist composition containing the salt as an acid generator.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP 2017-015777 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a salt capable ofproducing a resist pattern with line edge roughness (LER) which isbetter than that of a resist pattern formed from the above-mentionedresist composition containing the salt.

Means for Solving the Problems

The present invention includes the following inventions.

[1] A salt represented by formula (I):

wherein, in formula (I),

-   -   R¹, R², R³, R⁴ and R⁵ each independently represent a halogen        atom or a perfluoroalkyl group having 1 to 6 carbon atoms,    -   R⁶, R⁷ and R⁸ each independently represent a halogen atom, a        hydroxy group, a fluorinated alkyl group having 1 to 6 carbon        atoms or an alkyl group having 1 to 12 carbon atoms, and —CH₂—        included in the alkyl group may be replaced by —O— or —CO—,    -   m5 represents an integer of 1 to 5, and when m5 is 2 or more, a        plurality of R⁸ may be the same or different,    -   m6 represents an integer of 0 to 3, and when m6 is 2 or more, a        plurality of R^(E) may be the same or different,    -   m7 represents an integer of 0 to 3, and when m7 is 2 or more, a        plurality of R^(f) may be the same or different,    -   m8 represents an integer of 0 to 4, and when m8 is 2 or more, a        plurality of R⁸ may be the same or different, in which        1≤m5+m8≤5, and    -   AI⁻ represents an organic anion.        [2] The salt according to [1], wherein AI⁻ is a sulfonic acid        anion, a sulfonylimide anion, a sulfonylmethide anion and a        carboxylic acid anion.        [3] The salt according to [1] or [2], wherein AI⁻ is a sulfonic        acid anion and the sulfonic acid anion is an anion represented        by formula (I-A):

wherein, in formula (I-A),

-   -   Q¹ and Q² each independently represent a fluorine atom or a        perfluoroalkyl group having 1 to 6 carbon atoms,    -   L¹ represents a saturated hydrocarbon group having 1 to 24        carbon atoms, and —CH₂— included in the saturated hydrocarbon        group may be replaced by —O— or —CO—, and the hydrogen atom        included in the saturated hydrocarbon group may be substituted        with a fluorine atom or a hydroxy group, and    -   Y¹ represents a methyl group which may have a substituent or an        alicyclic hydrocarbon group having 3 to 18 carbon atoms which        may have a substituent, and —CH₂— included in the alicyclic        hydrocarbon group may be replaced by —O—, —SO— or —CO—.        [4] An acid generator comprising the salt according to any one        of [1] to [3].        [5] A resist composition comprising the acid generator according        to [4] and a resin having an acid-labile group.        [6] The resist composition according to [5], wherein a        structural unit having an acid-labile group includes at least        two of a structural unit represented by formula (a1-1) and a        structural unit represented by formula (a1-2):

wherein, in formula (a1-1) and formula (a1-2),

-   -   L^(a1) and L^(a2) each independently represent —O— or        *—O—(CH₂)_(k)1-CO—O—, k1 represents an integer of 1 to 7, and *        represents a bonding site to —CO—,    -   R^(a4) and R^(a5) each independently represent a hydrogen atom        or a methyl group,    -   R^(a6) and R^(a7) each independently represent an alkyl group        having 1 to 8 carbon atoms, an alicyclic hydrocarbon group        having 3 to 18 carbon atoms, or a group obtained by combining        these groups,    -   m1 represents an integer of 0 to 14,    -   n1 represents an integer of 0 to 10, and    -   n1′ represents an integer of 0 to 3.        [7] The resist composition according to [5] or [6], further        comprising a salt generating an acid having an acidity lower        than that of an acid generated from the acid generator.        [8] A method for producing a resist pattern, which comprises:    -   (1) a step of applying the resist composition according to any        one of [5] to [7] on a substrate,    -   (2) a step of drying the applied composition to form a        composition layer,    -   (3) a step of exposing the composition layer,    -   (4) a step of heating the exposed composition layer, and    -   (5) a step of developing the heated composition layer.

Effects of the Invention

It is possible to produce a resist pattern with satisfactory line edgeroughness (LER) by using a resist composition using a salt of thepresent invention.

MODE FOR CARRYING OUT THE INVENTION

In the present specification, “(meth)acrylic monomer” means at least oneselected from the group consisting of a monomer having a structure of“CH₂═CH—CO—” and a monomer having a structure of “CH₂═C(CH₃)—CO—”.Similarly, “(meth)acrylate” and “(meth)acrylic acid” each mean “at leastone selected from the group consisting of acrylate and methacrylate” and“at least one selected from the group consisting of acrylic acid andmethacrylic acid”. When a structural unit having “CH₂═C(CH₃)—CO—” or“CH═CH—CO—” is exemplified, it is a structural unit having both groupsshall be similarly exemplified. In groups mentioned in the presentspecification, regarding groups capable of having both a linearstructure and a branched structure, they may have either the linear orbranched structure. When stereoisomers exist, all stereoisomers areincluded.

In the present specification, “solid component of resist composition”means the total of components excluding the below-mentioned solvent (E)from the total amount of the resist composition.

<Salt Represented by Formula (I)>

The present invention relates to a salt represented by formula (I)(hereinafter sometimes referred to as “salt (I)”).

Among the salt (I), the side having negative charge is sometimesreferred to as “anion (I)”, and the side having positive charge issometimes referred to as “cation (I)”.

Examples of the halogen atom of R¹, R², R³, R⁴ and R⁵ include a fluorineatom, a chlorine atom, a bromine atom and an iodine atom.

Examples of the perfluoroalkyl group having 1 to 6 carbon atoms of R¹,R², R³, R⁴ and R⁵ include a trifluoromethyl group, a perfluoroethylgroup, a perfluoropropyl group, a perfluoroisopropyl group, aperfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butylgroup, a perfluoropentyl group, a perfluorohexyl group and the like.

R¹, R², R³, R⁴ and R⁵ each independently is preferably a perfluoroalkylgroup having 1 to 3 carbon atoms or a fluorine atom, more preferably atrifluoromethyl group or a fluorine atom, and still more preferably afluorine atom.

Examples of the fluorinated alkyl group having 1 to 6 carbon atoms ofR⁶, R⁷ and R⁸ include fluorinated alkyl groups such as a trifluoromethylgroup, a difluoromethyl group, a perfluoroethyl group,a2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, aperfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, aperfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutyl group, aperfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group and aperfluorohexyl group.

Examples of the alkyl group having 1 to 12 carbon atoms of R⁶, R⁷ and R⁸include alkyl groups such as a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, an isobutyl group, atert-butyl group, a pentyl group, a hexyl group, an octyl group and anonyl group. The number of carbon atoms of the alkyl group is preferably1 to 9, and more preferably 1 to 4.

When —CH₂— included in the alkyl group represented by R⁶, R⁷ and R⁸ isreplaced by —O— or —CO—, the number of carbon atoms before replacementis taken as the total number of carbon atoms of the alkyl group. Thealkyl group represented by R⁶, R⁷ and R⁸ may have a hydroxy group (groupin which —CH₂— included in a methyl group is replaced by —O—), acarboxyl group (group in which —CH₂—CH₂— included in an ethyl group isreplaced by —O—CO—), an alkoxy group having 1 to 6 carbon atoms (groupin which —CH₂— included in an alkyl group having 2 to 7 carbon atoms isreplaced by —O—), an alkoxycarbonyl group having 2 to 7 carbon atoms(group in which —CH₂—CH₂— included in an alkyl group having 4 to 9carbon atoms is replaced by —O—CO—), an alkylcarbonyl group having 2 to7 carbon atoms (group in which —CH₁— included in an alkyl group having 3to 8 carbon atoms is replaced by —CO—), or an alkylcarbonyloxy grouphaving 2 to 7 carbon atoms (group in which —CH₂—CH₂— included in analkyl group having 4 to 9 carbon atoms is replaced by —CO—O—).

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropoxy group, a butoxy group, a pentyloxy group and a hexyloxy group.

The alkoxycarbonyl group having 2 to 7 carbon atoms, the alkylcarbonylgroup having 2 to 7 carbon atoms and the alkylcarbonyloxy group having 2to 7 carbon atoms represent groups in which a carbonyl group or acarbonyloxy group is bonded to the above-mentioned alkyl group or alkoxygroup.

Examples of the alkoxycarbonyl group having 2 to 7 carbon atoms includea methoxycarbonyl group, an ethoxycarbonyl group and a butoxycarbonylgroup. Examples of the alkylcarbonyl group having 2 to 7 carbon atomsinclude an acetyl group, a propionyl group and a butyryl group. Examplesof the alkylcarbonyloxy group having 2 to 7 carbon atoms include anacetyloxy group, a propionyloxy group, a butyryloxy group and the like.

R⁶ and R⁷ each independently is preferably a fluorine atom, a hydroxygroup, a fluorinated alkyl group having 1 to 3 carbon atoms or an alkylgroup having 1 to 3 carbon atoms (—CH₂— included in the alkyl group maybe replaced by —O— or —CO—), more preferably a fluorine atom or atrifluoromethyl group, and still more preferably a fluorine atom.

R⁸ is preferably a fluorine atom, a hydroxy group, a fluorinated alkylgroup having 1 to 3 carbon atoms or an alkyl group having 1 to 3 carbonatoms (—CH₂— included in the alkyl group may be replaced by —O— or—CO—), more preferably a fluorine atom, a trifluoromethyl group, ahydroxy group, a methyl group, a methoxy group or a methylcarbonyloxygroup, and still more preferably a fluorine atom.

-   -   m6 and m7 each independently is preferably an integer of 0 to 2,        more preferably 0 or 1, and still more preferably 0.    -   m5 is preferably an integer of 1 to 3, and more preferably 1 or        2.    -   m8 is preferably an integer of 0 to 2, and more preferably 0 or        1.    -   As to m5 and m8, 1≤m5+m8≤4 is preferred, and 1≤m5+m8≤3 is more        preferred.

Examples of the cation (I) include the following cations.

Examples of the organic anion represented by AI⁻ include a sulfonic acidanion, a sulfonylimide anion, a sulfonylmethide anion and a carboxylicacid anion. The organic anion represented by AI⁻ is preferably asulfonic acid anion, and more preferably an anion represented by formula(I-A).

wherein, in formula (I-A),

-   -   Q¹ and Q² each independently represent a fluorine atom or a        perfluoroalkyl group having 1 to 6 carbon atoms,    -   L¹ represents a saturated hydrocarbon group having 1 to 24        carbon atoms, —CH₂— included in the saturated hydrocarbon group        may be replaced by —O— or —CO—, and a hydrogen atom included in        the saturated hydrocarbon group may be substituted with a        fluorine atom or a hydroxy group, and    -   Y¹ represents a methyl group which may have a substituent or an        alicyclic hydrocarbon group having 3 to 18 carbon atoms which        may have a substituent, and —CH₂— included in the alicyclic        hydrocarbon group may be replaced by —O—, —SO₂— or —CO—.

In formula (I-A), when —CH₂— included in a saturated hydrocarbon groupis replaced by —O— or —C(═O)—, the number of carbon atoms beforereplacement is taken as the number of carbon atoms of the saturatedhydrocarbon group. When —CH₂-included in an alicyclic hydrocarbon groupis replaced by —O—, —SO₂— or —C(═O)—, the number of carbon atoms beforereplacement is taken as the number of carbon atoms of the alicyclichydrocarbon group.

Examples of the perfluoroalkyl group having 1 to 6 carbon atoms of Q¹and Q² include a trifluoromethyl group, a perfluoroethyl group, aperfluoropropyl group, a perfluoroisopropyl group, a perfluorobutylgroup, a perfluorosec-butyl group, a perfluorotert-butyl group, aperfluoropentyl group and a perfluorohexyl group.

Preferably, Q¹ and Q² are each independently a fluorine atom ortrifluoromethyl group, and more preferably, both are fluorine atoms.

Examples of the divalent saturated hydrocarbon group in L¹ include alinear alkanediyl group, a branched alkanediyl group, and a monocyclicor polycyclic divalent alicyclic saturated hydrocarbon group, or thedivalent saturated hydrocarbon group may be a group formed by combiningtwo or more of these groups.

Specific examples thereof include linear alkanediyl groups such as amethylene group, an ethylene group, a propane-1,3-diyl group, abutane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diylgroup, a heptane-1,7-diyl group, an octane-1,8-diyl group, anonane-1,9-diyl group, a decane-1,10-diyl group, an undecane-1,11-diylgroup, a dodecane-1,12-diyl group, a tridecane-1,13-diyl group, atetradecane-1,14-diyl group, a pentadecane-1,15-diyl group, ahexadecane-1,16-diyl group and a heptadecane-1,17-diyl group;

branched alkanediyl groups such as an ethane-1,1-diyl group, apropane-1,1-diyl group, a propane-1,2-diyl group, a propane-2,2-diylgroup, a pentane-2,4-diyl group, a 2-methylpropane-1,3-diyl group, a2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group and a2-methylbutane-1,4-diyl group;

monocyclic divalent alicyclic saturated hydrocarbon groups which arecycloalkanediyl groups such as a cyclobutane-1,3-diyl group, acyclopentane-1,3-diyl group, a cyclohexane-1,4-diyl group and acyclooctane-1,5-diyl group; and

polycyclic divalent alicyclic saturated hydrocarbon groups such as anorbornane-1,4-diyl group, a norbornane-2,5-diyl group, anadamantane-1,5-diyl group and an adamantane-2,6-diyl group.

The group in which —CH— included in the divalent saturated hydrocarbongroup represented by L³ is replaced by —O— or —CO— includes, forexample, a group represented by any one of formula (b1-1) to formula(b1-3). In groups represented by formula (b1-1) to formula (b1-3) andgroups represented by formula (b1-4) to formula (b1-11) which arespecific examples thereof, * and ** represent a bonding site, and *represents a bonding site to —Y¹.

In formula (b1-1),

-   -   L^(b2) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom,    -   L^(b3) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 22 carbon atoms, a hydrogen atom        included in the saturated hydrocarbon group may be substituted        with a fluorine atom or a hydroxy group, and —CH₂— included in        the saturated hydrocarbon group may be replaced by —O— or —CO—,        and    -   the total number of carbon atoms of L^(b2) and L^(b3) is 22 or        less.

In formula (b1-2),

-   -   L^(b4) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom,    -   L^(b5) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 22 carbon atoms, a hydrogen atom        included in the saturated hydrocarbon group may be substituted        with a fluorine atom or a hydroxy group, and —CH₂— included in        the saturated hydrocarbon group may be replaced by —O— or —CO—,        and    -   the total number of carbon atoms of L^(b4) and L^(b5) is 22 or        less.

In formula (b1-3),

-   -   L^(b6) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 23 carbon atoms, a hydrogen atom        included in the saturated hydrocarbon group may be substituted        with a fluorine atom or a hydroxy group,    -   L^(b7) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 23 carbon atoms, a hydrogen atom        included in the saturated hydrocarbon group may be substituted        with a fluorine atom or a hydroxy group, and —CH₂— included in        the saturated hydrocarbon group may be replaced by —O— or —CO—,        and    -   the total number of carbon atoms of L^(b6) and L^(b7) is 23 or        less.

In groups represented by formula (b1-1) to formula (b1-3), when —CH₂—included in the saturated hydrocarbon group is replaced by —O— or —CO—,the number of carbon atoms before replacement is taken as the number ofcarbon atoms of the saturated hydrocarbon group.

Examples of the divalent saturated hydrocarbon group include those whichare the same as the divalent saturated hydrocarbon group of L^(b1).

-   -   L^(b2) is preferably a single bond.    -   L^(b3) is preferably a divalent saturated hydrocarbon group        having 1 to 4 carbon atoms.    -   L^(b4) is preferably a divalent saturated hydrocarbon group        having 1 to 8 carbon atoms, and a hydrogen atom included in the        divalent saturated hydrocarbon group may be substituted with a        fluorine atom.    -   L^(b5) is preferably a single bond or a divalent saturated        hydrocarbon group having 1 to 8 carbon atoms.    -   L^(b6) is preferably a single bond or a divalent saturated        hydrocarbon group having 1 to 4 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom.    -   L^(b7) is preferably a single bond or a divalent saturated        hydrocarbon group having 1 to 18 carbon atoms, a hydrogen atom        included in the saturated hydrocarbon group may be substituted        with a fluorine atom or a hydroxy group, and —CH₂— included in        the divalent saturated hydrocarbon group may be replaced by —O—        or —CO—.

The group in which —CH₂— included in the divalent saturated hydrocarbongroup represented by L¹ is replaced by —O— or —CO— is preferably a grouprepresented by formula (b1-1) or formula (b1-3).

Examples of the group represented by formula (b1-1) include groupsrepresented by formula (b1-4) to formula (b1-8).

In formula (b1-4),

-   -   L^(b8) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom or a hydroxy group.

In formula (b1-5),

-   -   L^(b9) represents a divalent saturated hydrocarbon group having        1 to 20 carbon atoms, and —CH₂— included in the divalent        saturated hydrocarbon group may be replaced by —O— or —CO—.    -   L^(b10) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 19 carbon atoms, and a hydrogen        atom included in the divalent saturated hydrocarbon group may be        substituted with a fluorine atom or a hydroxy group, and    -   the total number of carbon atoms of L^(b9) and L^(b10) is 20 or        less.

In formula (b1-6),

-   -   L^(b11) represents a divalent saturated hydrocarbon group having        1 to 21 carbon atoms,    -   L^(b12) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 20 carbon atoms, and a hydrogen        atom included in the divalent saturated hydrocarbon group may be        substituted with a fluorine atom or a hydroxy group, and    -   the total number of carbon atoms of L^(b11) and L^(b12) is 21 or        less.

In formula (b1-7),

-   -   L^(b13) represents a divalent saturated hydrocarbon group having        1 to 19 carbon atoms,    -   L^(b14) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 18 carbon atoms, and —CH₂—        included in the divalent saturated hydrocarbon group may be        replaced by —O— or —CO—,    -   L^(b15) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 18 carbon atoms, and a hydrogen        atom included in the divalent saturated hydrocarbon group may be        substituted with a fluorine atom or a hydroxy group, and    -   the total number of carbon atoms of L^(b13) to L^(b15) is 19 or        less.

In formula (b1-8),

-   -   L^(b16) represents a divalent saturated hydrocarbon group having        1 to 18 carbon atoms, and —CH₂— included in the divalent        saturated hydrocarbon group may be replaced by —O— or —CO—,    -   L^(b17) represents a divalent saturated hydrocarbon group having        1 to 18 carbon atoms,    -   L^(b18) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 17 carbon atoms, and a hydrogen        atom included in the divalent saturated hydrocarbon group may be        substituted with a fluorine atom or a hydroxy group, and    -   the total number of carbon atoms of L^(b16) to L^(b18) is 19 or        less.    -   L^(b3) is preferably a divalent saturated hydrocarbon group        having 1 to 4 carbon atoms.    -   L^(b9) is preferably a divalent saturated hydrocarbon group        having 1 to 8 carbon atoms.    -   L^(b10) is preferably a single bond or a divalent saturated        hydrocarbon group having 1 to 19 carbon atoms, and more        preferably a single bond or a divalent saturated hydrocarbon        group having 1 to 8 carbon atoms.    -   L^(b11) is preferably a divalent saturated hydrocarbon group        having 1 to 8 carbon atoms.    -   L^(b12) is preferably a single bond or a divalent saturated        hydrocarbon group having 1 to 8 carbon atoms.    -   L^(b13) is preferably a divalent saturated hydrocarbon group        having 1 to 12 carbon atoms.    -   L^(b14) is preferably a single bond or a divalent saturated        hydrocarbon group having 1 to 6 carbon atoms.    -   L^(b15) is preferably a single bond or a divalent saturated        hydrocarbon group having 1 to 18 carbon atoms, and more        preferably a single bond or a divalent saturated hydrocarbon        group having 1 to 8 carbon atoms.    -   L^(b16) is preferably a divalent saturated hydrocarbon group        having 1 to 12 carbon atoms.    -   L^(b17) is preferably a divalent saturated hydrocarbon group        having 1 to 6 carbon atoms.    -   L^(b18) is preferably a single bond or a divalent saturated        hydrocarbon group having 1 to 17 carbon atoms, and more        preferably a single bond or a divalent saturated hydrocarbon        group having 1 to 4 carbon atoms.

Examples of the group represented by formula (b1-3) include groupsrepresented by formula (b1-9) to formula (b1-11).

In formula (b1-9),

-   -   L^(b13) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 23 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom,    -   L^(b20) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 23 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom, a hydroxy group or an        alkylcarbonyloxy group, —CH₂— included in the alkylcarbonyloxy        group may be replaced by —O— or —CO—, and a hydrogen atom        included in the alkylcarbonyloxy group may be substituted with a        hydroxy group, and    -   the total number of carbon atoms of L^(b15) and L^(b20) is 23 or        less.

In formula (b1-10),

-   -   L^(b21) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 21 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom,    -   L^(b22) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 21 carbon atoms,    -   L^(b23) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 21 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom, a hydroxy group or an        alkylcarbonyloxy group, —CH₂— included in the alkylcarbonyloxy        group may be replaced by —O— or —CO—, and a hydrogen atom        included in the alkylcarbonyloxy group may be substituted with a        hydroxy group, and    -   the total number of carbon atoms of L^(b21), L^(b22) and L^(b23)        is 21 or less.

In formula (b1-11),

-   -   L^(b24) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 20 carbon atoms, and a hydrogen        atom included in the saturated hydrocarbon group may be        substituted with a fluorine atom,    -   L^(b25) represents a divalent saturated hydrocarbon group having        1 to 21 carbon atoms,    -   L^(b26) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 20 carbon atoms, a hydrogen atom        included in the saturated hydrocarbon group may be substituted        with a fluorine atom, a hydroxy group or an alkylcarbonyloxy        group, —CH₂— included in the alkylcarbonyloxy group may be        replaced by —O— or —CO—, and a hydrogen atom included in the        alkylcarbonyloxy group may be substituted with a hydroxy group,        and    -   the total number of carbon atoms of L^(b24), L^(b25) and L^(b26)        is 21 or less.

In groups represented by formula (b1-9) to formula (b1-11), when ahydrogen atom included in the saturated hydrocarbon group is substitutedwith an alkylcarbonyloxy group, the number of carbon atoms beforesubstitution is taken as the number of carbon atoms of the saturatedhydrocarbon group.

Examples of the alkylcarbonyloxy group include an acetyloxy group, apropionyloxy group, a butyryloxy group, a cyclohexylcarbonyloxy group,an adamantylcarbonyloxy group and the like.

Examples of the group represented by formula (b1-4) include thefollowings:

Examples of the group represented by formula (b1-5) include thefollowings:

Examples of the group represented by formula (b1-6) include thefollowings:

Examples of the group represented by formula (b1-7) include thefollowings:

Examples of the group represented by formula (b1-8) include thefollowings:

Examples of the group represented by formula (b1-2) include thefollowings:

Examples of the group represented by formula (b1-9) include thefollowings:

Examples of the group represented by formula (b1-10) include thefollowings:

Examples of the group represented by formula (b1-11) include thefollowings:

Examples of the alicyclic hydrocarbon group represented by Y¹ includegroups represented by formula (Y1) to formula (Y11) and formula (Y36) toformula (Y38).

When —CH₂— included in the alicyclic hydrocarbon group represented by Y¹is replaced by —O—, —S(O)₂— or —CO—, the number may be 1, or 2 or more.Examples of such group include groups represented by formula (Y12) toformula (Y35) and formula (Y39) to formula (Y41). * represents a bondingsite to L¹.

An alicyclic hydrocarbon group represented by Y¹ is preferably a grouprepresented by any one of formula (Y1) to formula (Y20), formula (Y26),formula (Y27), formula (Y30), formula (Y31) and formula (Y39) to formula(Y41), more preferably a group represented by formula (Y11), formula(Y15), formula (Y16), formula (Y20), formula (Y26), formula (Y27),formula (Y30), formula (Y31), formula (Y39) or formula (Y40), and stillmore preferably a group represented by formula (Y11), formula (Y15),formula (Y20), formula (Y30), formula (Y39) or formula (Y40).

When an alicyclic hydrocarbon group represented by Y¹ is a spiro ringsuch as formula (Y28) to formula (Y35), the alkanediyl group between twooxygen atoms preferably includes one or more fluorine atoms. Amongalkanediyl groups included in a ketal structure, it is preferred that amethylene group adjacent to the oxygen atom is not substituted with afluorine atom.

Examples of the substituent of the methyl group represented by Y¹include a halogen atom, a hydroxy group, an alicyclic hydrocarbon grouphaving 3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to18 carbon atoms, a glycidyloxy group, a —(CH²)_(ja)—CO—O—R^(b1) group ora —(CH₂)_(ja)—O—CO—R^(b1) group (wherein R^(b1) represents an alkylgroup having 1 to 16 carbon atoms, an alicyclic hydrocarbon group having3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18carbon atoms, or groups obtained by combining these groups, jarepresents an integer of 0 to 4, and —CH₂-included in an alkyl grouphaving 1 to 16 carbon atoms and an alicyclic hydrocarbon group having 3to 16 carbon atoms may be replaced by —O—, —S(O)₂— or —CO—) and thelike.

Examples of the substituent of the alicyclic hydrocarbon grouprepresented by Y¹ include a halogen atom, a hydroxy group, an alkylgroup having 1 to 12 carbon atoms which may be substituted with ahydroxy group, an alicyclic hydrocarbon group having 3 to 16 carbonatoms, an alkoxy group having 1 to 12 carbon atoms, an aromatichydrocarbon group having 6 to 18 carbon atoms, an aralkyl group having 7to 21 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, aglycidyloxy group, a —(CH₂)_(ja)—CO—O—R^(b1) group or—(CH₂)_(ja)—O—CO—R^(b1) group (wherein R^(b1) represents an alkyl grouphaving 1 to 16 carbon atoms, an alicyclic hydrocarbon group having 3 to16 carbon atoms or an aromatic hydrocarbon group having 6 to 18 carbonatoms, or groups obtained by combining these groups, ja represents aninteger of 0 to 4, and —CH₂— included in the alkyl group having 1 to 16carbon atoms and the alicyclic hydrocarbon group having 3 to 16 carbonatoms may be replaced by —O—, —S(O)₂— or —CO—) and the like.

Examples of the halogen atom include a fluorine atom, a chlorine atom, abromine atom and an iodine atom.

The alicyclic hydrocarbon group includes, for example, a cyclopentylgroup, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, anorbornyl group, an adamantyl group and the like. The alicyclichydrocarbon group may have a chain hydrocarbon group, and examplesthereof include a methylcyclohexyl group, a dimethylcyclohexyl group andthe like.

The aromatic hydrocarbon group includes, for example, aryl groups suchas a phenyl group, a naphthyl group, an anthryl group, a biphenyl group,and a phenanthryl group. The aromatic hydrocarbon group may have a chainhydrocarbon group or an alicyclic hydrocarbon group and examples thereofinclude an aromatic hydrocarbon group having a chain hydrocarbon grouphaving 1 to 18 carbon atoms (a tolyl group, a xylyl group, a cumenylgroup, a mesityl group, a p-methylphenyl group, a p-ethylphenyl group, ap-tert-butylphenyl group, a 2,6-diethylphenyl group, a2-methyl-6-ethylphenyl group, etc.) and an aromatic hydrocarbon grouphaving alicyclic hydrocarbon group having 3 to 18 carbon atoms (ap-cyclohexylphenyl group, a p-adamantylphenyl group, etc.).

The alkyl group includes, for example, a methyl group, an ethyl group, apropyl group, an isopropyl group, a butyl group, a sec-butyl group, atert-butyl group, a pentyl group, a hexyl group, a heptyl group, a2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, anundecyl group, a dodecyl group and the like.

Examples of the alkyl group substituted with a hydroxy group includehydroxyalkyl groups such as a hydroxymethyl group and a hydroxyethylgroup.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, aheptyloxy group, an octyloxy group, a decyloxy group and a dodecyloxygroup.

Examples of the aralkyl group include a benzyl group, a phenethyl group,a phenylpropyl group, a naphthylmethyl group and a naphthylethyl group.

The alkylcarbonyl group includes, for example, an acetyl group, apropionyl group and a butyryl group.

Examples of Y¹ include the followings.

Y¹ is preferably an alicyclic hydrocarbon group having 3 to 18 carbonatoms which may have a substituent, more preferably an alicyclichydrocarbon group substituted with a hydroxy group, and still morepreferably an adamantyl group which may have a substituent, and —CH₂—constituting the alicyclic hydrocarbon group or the adamantyl group maybe replaced by —CO—, —S(O)₂— or —CO—. Y¹ is still more preferably anadamantyl group, a hydroxyadamantyl group, an oxoadamantyl group, orgroups represented by the followings, and particularly preferably ahydroxyadamantyl group or an oxoadamantyl group, or groups includingthese groups.

The anion represented by formula (I-A) is preferably anions representedby formula (I-A-1) to formula (I-A-55) [hereinafter sometimes referredto as “anion (I-A-1)” according to the number of formula], and morepreferably an anion represented by any one of formula (I-A-1) to formula(I-A-4), formula (I-A-9), formula (I-A-10), formula (I-A-24) to formula(I-A-33), formula (I-A-36) to formula (I-A-40) and formula (I-A-47) toformula (I-A-55).

R^(i2) to R^(i7) each independently represent, for example, an alkylgroup having 1 to 4 carbon atoms, and preferably a methyl group or anethyl group. R^(i8) is, for example, a chain hydrocarbon group having 1to 12 carbon atoms, preferably an alkyl group having 1 to 4 carbonatoms, an alicyclic hydrocarbon group having 5 to 12 carbon atoms orgroups formed by combining these groups, and more preferably a methylgroup, an ethyl group, a cyclohexyl group or an adamantyl group. L^(A41)is a single bond or an alkanediyl group having 1 to 4 carbon atoms. Q¹and Q² are the same as defined above.

Specific examples of the anion represented by formula (I-A) includeanions mentioned in JP 2010-204646 A.

Examples of the anion represented by formula (I-A) are preferably anionsrepresented by formula (I-a-1) to formula (I-a34).

Among these, an anion represented by any one of formula (I-a-1) toformula (I-a-3) and formula (I-a-7) to formula (I-a-19) and formula(I-a-22) to formula (I-a-34) is preferable.

Examples of the sulfonylimide anion represented by AI⁻ include thefollowings.

Examples of the sulfonylmethide anion include the followings.

Examples of the carboxylic acid anion include the followings.

Specific examples of the salt (I) include salts obtained by optionallycombining the above-mentioned cations and anions. Specific examples ofthe salt (I) are shown in the following Table.

In the following Table, each symbol represents a symbol attached to astructure which represents the above-mentioned anion and cation. Forexample, the salt (I-1) is a salt composed of an anion represented byformula (I-a-1) and a cation represented by formula (I-c-1) and is thefollowing salt.

TABLE 1 Salt (I) Anion (I) Cation (I) (I-1) (I-a-1) (I-c-1) (I-2)(I-a-2) (I-c-1) (I-3) (I-a-3) (I-c-1) (I-4) (I-a-7) (I-c-1) (I-5)(I-a-8) (I-c-1) (I-6) (I-a-9) (I-c-1) (I-7) (I-a-10) (I-c-1) (I-8)(I-a-11) (I-c-1) (I-9) (I-a-12) (I-c-1) (I-10) (I-a-13) (I-c-1) (I-11)(I-a-14) (I-c-1) (I-12) (I-a-15) (I-c-1) (I-13) (I-a-16) (I-c-1) (I-14)(I-a-17) (I-c-1) (I-15) (I-a-18) (I-c-1) (I-16) (I-a-19) (I-c-1) (I-17)(I-a-22) (I-c-1) (I-18) (I-a-23) (I-c-1) (I-19) (I-a-24) (I-c-1) (I-20)(I-a-25) (I-c-1) (I-21) (I-a-26) (I-c-1) (I-22) (I-a-27) (I-c-1) (I-23)(I-a-28) (I-c-1) (I-24) (I-a-29) (I-c-1) (I-25) (I-a-30) (I-c-1) (I-26)(I-a-31) (I-c-1) (I-27) (I-a-32) (I-c-1) (I-28) (I-a-33) (I-c-1) (I-29)(I-a-34) (I-c-1) (I-30) (I-a-1) (I-c-2) (I-31) (I-a-2) (I-c-2) (I-32)(I-a-3) (I-c-2) (I-33) (I-a-7) (I-c-2) (I-34) (I-a-8) (I-c-2) (I-35)(I-a-9) (I-c-2) (I-36) (I-a-10) (I-c-2) (I-37) (I-a-11) (I-c-2) (I-38)(I-a-12) (I-c-2) (I-39) (I-a-13) (I-c-2) (I-40) (I-a-14) (I-c-2) (I-41)(I-a-15) (I-c-2) (I-42) (I-a-16) (I-c-2) (I-43) (I-a-17) (I-c-2) (I-44)(I-a-18) (I-c-2) (I-45) (I-a-19) (I-c-2) (I-46) (I-a-22) (I-c-2) (I-47)(I-a-23) (I-c-2) (I-48) (I-a-24) (I-c-2) (I-49) (I-a-25) (I-c-2) (I-50)(I-a-26) (I-c-2) (I-51) (I-a-27) (I-c-2) (I-52) (I-a-28) (I-c-2) (I-53)(I-a-29) (I-c-2) (I-54) (I-a-30) (I-c-2) (I-55) (I-a-31) (I-c-2) (I-56)(I-a-32) (I-c-2) (I-57) (I-a-33) (I-c-2) (I-58) (I-a-34) (I-c-2) (I-59)(I-a-1) (I-c-3) (I-60) (I-a-2) (I-c-3) (I-61) (I-a-3) (I-c-3) (I-62)(I-a-7) (I-c-3) (I-63) (I-a-8) (I-c-3) (I-64) (I-a-9) (I-c-3) (I-65)(I-a-10) (I-c-3) (I-66) (I-a-11) (I-c-3) (I-67) (I-a-12) (I-c-3) (I-68)(I-a-13) (I-c-3) (I-69) (I-a-14) (I-c-3) (I-70) (I-a-15) (I-c-3) (I-71)(I-a-16) (I-c-3) (I-72) (I-a-17) (I-c-3) (I-73) (I-a-18) (I-c-3) (I-74)(I-a-19) (I-c-3) (I-75) (I-a-22) (I-c-3) (I-76) (I-a-23) (I-c-3) (I-77)(I-a-24) (I-c-3) (I-78) (I-a-25) (I-c-3) (I-79) (I-a-26) (I-c-3) (I-80)(I-a-27) (I-c-3) (I-81) (I-a-28) (I-c-3) (I-82) (I-a-29) (I-c-3) (I-83)(I-a-30) (I-c-3) (I-84) (I-a-31) (I-c-3) (I-85) (I-a-32) (I-c-3) (I-86)(I-a-33) (I-c-3) (I-87) (I-a-34) (I-c-3) (I-88) (I-a-1) (I-c-4) (I-89)(I-a-2) (I-c-4) (I-90) (I-a-3) (I-c-4) (I-91) (I-a-7) (I-c-4) (I-92)(I-a-8) (I-c-4) (I-93) (I-a-9) (I-c-4) (I-94) (I-a-10) (I-c-4) (I-95)(I-a-11) (I-c-4) (I-96) (I-a-12) (I-c-4) (I-97) (I-a-13) (I-c-4) (I-98)(I-a-14) (I-c-4) (I-99) (I-a-15) (I-c-4) (I-100) (I-a-16) (I-c-4)(I-101) (I-a-17) (I-c-4) (I-102) (I-a-18) (I-c-4) (I-103) (I-a-19)(I-c-4) (I-104) (I-a-22) (I-c-4) (I-105) (I-a-23) (I-c-4) (I-106)(I-a-24) (I-c-4) (I-107) (I-a-25) (I-c-4) (I-108) (I-a-26) (I-c-4)(I-109) (I-a-27) (I-c-4) (I-110) (I-a-28) (I-c-4) (I-111) (I-a-29)(I-c-4) (I-112) (I-a-30) (I-c-4) (I-113) (I-a-31) (I-c-4) (I-114)(I-a-32) (I-c-4) (I-115) (I-a-33) (I-c-4) (I-116) (I-a-34) (I-c-4)(I-117) (I-a-1) (I-c-5) (I-118) (I-a-2) (I-c-5) (I-119) (I-a-3) (I-c-5)(I-120) (I-a-7) (I-c-5) (I-121) (I-a-8) (I-c-5) (I-122) (I-a-9) (I-c-5)(I-123) (I-a-10) (I-c-5) (I-124) (I-a-11) (I-c-5) (I-125) (I-a-12)(I-c-5) (I-126) (I-a-13) (I-c-5) (I-127) (I-a-14) (I-c-5) (I-128)(I-a-15) (I-c-5) (I-129) (I-a-16) (I-c-5) (I-130) (I-a-17) (I-c-5)(I-131) (I-a-18) (I-c-5) (I-132) (I-a-19) (I-c-5) (I-133) (I-a-22)(I-c-5) (I-134) (I-a-23) (I-c-5) (I-135) (I-a-24) (I-c-5) (I-136)(I-a-25) (I-c-5) (I-137) (I-a-26) (I-c-5) (I-138) (I-a-27) (I-c-5)(I-139) (I-a-28) (I-c-5) (I-140) (I-a-29) (I-c-5) (I-141) (I-a-30)(I-c-5) (I-142) (I-a-31) (I-c-5) (I-143) (I-a-32) (I-c-5) (I-144)(I-a-33) (I-c-5) (I-145) (I-a-34) (I-c-5)

Among these salts, the salt (I) preferably include salt (I-1) to salt(I-5), salt (I-13) to salt (I-25), salt (I-30) to salt (I-34), salt(I-42) to salt (I-54), salt (I-59) to salt (I-63), salt (I-71) to salt(I-83), salt (I-88) to salt (I-92), salt (I-100) to salt (I-112), salt(I-117) to salt (I-121) and salt (I-129) to salt (I-141).

<Method for Producing Salt (I)>

The salt (I) can be produced by reacting a salt represented by formula(I-a) with a salt represented by formula (I-b) in a solvent:

wherein all symbols are the same as defined above.

Examples of the solvent include chloroform, monochlorobenzene,acetonitrile, water and the like.

The reaction temperature is usually 15° C. to 80° C., and the reactiontime is usually 0.5 to 24 hours.

Examples of the salt represented by formula (I-b) include saltsrepresented by the following formulas. These salts can be obtained bythe method mentioned in JP 2011-116747 A.

A salt represented by formula (I-a) can be produced by reacting acompound represented by formula (I-c) with a Grignard compound, which isobtained by reacting magnesium with a compound represented by formula(I-d) in a solvent, in the presence of trimethylchlorosilane and a basein a solvent, followed by further reaction with dimethylsulfuric acid:

wherein all symbols are the same as defined above.

Examples of the solvent include tetrahydrofuran and the like.

Examples of the base include triethylamine and the like.

The reaction temperature is usually 5° C. to 80° C., and the reactiontime is usually 0.5 to 24 hours.

The compound represented by formula (I-c) includes a compoundrepresented by the following formula and can be obtained by the samemethod as mentioned in JP 2017-015777 A.

The compound represented by formula (I-d) include compounds representedby the followings and is easily available on the market.

<Acid Generator>

The acid generator of the present invention is an acid generatorincluding the salt (I). The acid generator may include one salt (I) ormay include two or more salts (I).

The acid generator of the present invention may include, in addition tothe salt (I), an acid generator known in the resist field (hereinaftersometimes referred to as “acid generator (B)”). The acid generator (B)may be used alone, or two or more acid generators may be used incombination.

Either nonionic or ionic acid generator may be used as the acidgenerator (B). Examples of the nonionic acid generator include sulfonateesters (e.g. 2-nitrobenzyl ester, aromatic sulfonate, oxime sulfonate,N-sulfonyloxyimide, sulfonyloxyketone, diazonaphthoquinone 4-sulfonate),sulfones (e.g. disulfone, ketosulfone, sulfonyldiazomethane) and thelike. Typical examples of the ionic acid generator include onium saltscontaining an onium cation (e.g. diazonium salt, phosphonium salt,sulfonium salt, iodonium salt). Examples of the anion of the onium saltinclude sulfonic acid anion, sulfonylimide anion, sulfonylmethide anionand the like.

Specific examples of the acid generator (B) include compounds generatingan acid upon exposure to radiation mentioned in JP 63-26653 A, JP55-164824 A, JP 62-69263 A, JP 63-146038 A, JP 63-163452 A, JP 62-153853A, JP 63-146029 A, U.S. Pat. Nos. 3,779,778, 3,849,137, DE Patent No.3914407 and EP Patent No. 126,712. Compounds produced by a known methodmay also be used. Two or more acid generators (B) may also be used incombination.

The acid generator (B) is preferably a fluorine-containing acidgenerator, and more preferably a salt represented by formula (B1)(hereinafter sometimes referred to as “acid generator (B1)”):

wherein, in formula (B1),

-   -   Q^(b1) and Q^(b2) each independently represent a fluorine atom        or a perfluoroalkyl group having 1 to 6 carbon atoms,    -   L^(b1) represents a saturated hydrocarbon group having 1 to 24        carbon atoms, —CH₂— included in the saturated hydrocarbon group        may be replaced by —O— or —CO—, and a hydrogen atom included in        the saturated hydrocarbon group may be substituted with a        fluorine atom or a hydroxy group,    -   Y represents a methyl group which may have a substituent or an        alicyclic hydrocarbon group having 3 to 18 carbon atoms which        may have a substituent, and —CH₂— included in the alicyclic        hydrocarbon group may be replaced by —O—, —S(O)₂— or —CO—, and    -   Z1⁺ represents an organic cation.

Examples of Q^(b1), Q^(b2), L^(b1) and Y in formula (B1) include thosewhich are respectively the same as the above-mentioned Q¹, Q², L¹ and Y¹in formula (I-A).

Examples of the sulfonic acid anion in formula (B1) include those whichare the same as the anion represented by formula (I-A).

Examples of the organic cation of Z1⁺ include an organic onium cation,an organic sulfonium cation, an organic iodonium cation, an organicammonium cation, a benzothiazolium cation and an organic phosphoniumcation. Among these organic cations, an organic sulfonium cation and anorganic iodonium cation are preferred, and an arylsulfonium cation ismore preferred. Specific examples thereof include a cation representedby any one of formula (b2-1) to formula (b2-4) (hereinafter sometimesreferred to as “cation (b2-1)” according to the number of formula).

In formula (b2-1) to formula (b2-4),

-   -   R^(b4) to R^(b6) each independently represent a chain        hydrocarbon group having 1 to 30 carbon atoms, an alicyclic        hydrocarbon group having 3 to 36 carbon atoms or an aromatic        hydrocarbon group having 6 to 36 carbon atoms, a hydrogen atom        included in the chain hydrocarbon group may be substituted with        a hydroxy group, an alkoxy group having 1 to 12 carbon atoms, an        alicyclic hydrocarbon group having 3 to 12 carbon atoms or an        aromatic hydrocarbon group having 6 to 18 carbon atoms, a        hydrogen atom included in the alicyclic hydrocarbon group may be        substituted with a halogen atom, an aliphatic hydrocarbon group        having 1 to 18 carbon atoms, an alkylcarbonyl group having 2 to        4 carbon atoms or a glycidyloxy group, and a hydrogen atom        included in the aromatic hydrocarbon group may be substituted        with a halogen atom, a hydroxy group or an alkoxy group having 1        to 12 carbon atoms,    -   R^(b4) and R^(b5) may be bonded to each other to form a ring        together with sulfur atoms to which R^(b4) and R^(b5), are        bonded, and —CH₂— included in the ring may be replaced by —O—,        —S— or —CO—,    -   R^(b7) and R^(b8) each independently represent a hydroxy group,        an aliphatic hydrocarbon group having 1 to 12 carbon atoms or an        alkoxy group having 1 to 12 carbon atoms,    -   m2 and n2 each independently represent an integer of 0 to 5,    -   when m2 is 2 or more, a plurality of R^(b7) may be the same or        different, and when n2 is 2 or more, a plurality of R^(b8) may        be the same or different,    -   R^(b9) and R^(b10) each independently represent a chain        hydrocarbon group having 1 to 36 carbon atoms or an alicyclic        hydrocarbon group having 3 to 36 carbon atoms,    -   R^(b9) and R^(b10) may be bonded to each other to form a ring        together with sulfur atoms to which R^(b9) and R^(b10) are        bonded, and —CH₂— included in the ring may be replaced by —O—,        —S— or —CO—,    -   R^(b11) represents a hydrogen atom, a chain hydrocarbon group        having 1 to 36 carbon atoms, an alicyclic hydrocarbon group        having 3 to 36 carbon atoms or an aromatic hydrocarbon group        having 6 to 18 carbon atoms,    -   R^(b12) represents a chain hydrocarbon group having 1 to 12        carbon atoms, an alicyclic hydrocarbon group having 3 to 18        carbon atoms or an aromatic hydrocarbon group having 6 to 18        carbon atoms, a hydrogen atom included in the chain hydrocarbon        may be substituted with an aromatic hydrocarbon group having 6        to 18 carbon atoms, and a hydrogen atom included in the aromatic        hydrocarbon group may be substituted with an alkoxy group having        1 to 12 carbon atoms or an alkylcarbonyloxy group having 1 to 12        carbon atoms,    -   R^(b11) and R^(b12) may be bonded to each other to form a ring,        including —CH—CO— to which R^(b11) and R¹² are bonded, and —CH₂—        included in the ring may be replaced by —O—, —S— or —CO—,    -   R^(b13) to R^(b18) each independently represent a hydroxy group,        an aliphatic hydrocarbon group having 1 to 12 carbon atoms or an        alkoxy group having 1 to 12 carbon atoms,    -   L^(b31) represents a sulfur atom or an oxygen atom,    -   o2, p2, s2 and t2 each independently represent an integer of 0        to 5,    -   q2 and r2 each independently represent an integer of 0 to 4,    -   u2 represents 0 or 1, and    -   when o2 is 2 or more, a plurality of R^(b13) are the same or        different, when p2 is 2 or more, a plurality of R^(b14) are the        same or different, when q2 is 2 or more, a plurality of R^(b15)        are the same or different, when r2 is 2 or more, a plurality of        R^(b16) are the same or different, when s2 is 2 or more, a        plurality of R^(b17) are the same or different, and when t2 is 2        or more, a plurality of R^(b18) are the same or different.

The aliphatic hydrocarbon group represents a chain hydrocarbon group andan alicyclic hydrocarbon group.

Examples of the chain hydrocarbon group include alkyl groups such as amethyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, ahexyl group, an octyl group and a 2-ethylhexyl group. Particularly, thechain hydrocarbon group for R^(b9) to R^(b12) preferably has 1 to 12carbon atoms.

The alicyclic hydrocarbon group may be either monocyclic or polycyclic,and examples of the monocyclic alicyclic hydrocarbon group includecycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, acyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctylgroup and a cyclodecyl group. Examples of the polycyclic alicyclichydrocarbon group include a decahydronaphthyl group, an adamantyl group,a norbornyl group and the following groups.

Particularly, the alicyclic hydrocarbon group for R^(b9) to R^(b12)preferably has 3 to 18 carbon atoms, and more preferably 4 to 12 carbonatoms.

Examples of the alicyclic hydrocarbon group in which a hydrogen atom issubstituted with an aliphatic hydrocarbon group include amethylcyclohexyl group, a dimethylcyclohexyl group, a2-methyladamantan-2-yl group, a 2-ethyladamantan-2-yl group, a2-isopropyladamantan-2-yl group, a methylnorbornyl group, an isobornylgroup and the like. In the alicyclic hydrocarbon group in which ahydrogen atom is substituted with an aliphatic hydrocarbon group, thetotal number of carbon atoms of the alicyclic hydrocarbon group and thealiphatic hydrocarbon group is preferably 20 or less.

Examples of the aromatic hydrocarbon group include aryl groups such as aphenyl group, a biphenyl group, a naphthyl group, an anthryl group and aphenanthryl group. The aromatic hydrocarbon group may have a chainhydrocarbon group or a alicyclic hydrocarbon group and examples thereofinclude an aromatic hydrocarbon group having a chain hydrocarbon group(a tolyl group, a xylyl group, a cumenyl group, a mesityl group, ap-ethylphenyl group, a p-tert-butylphenyl group, a 2,6-diethylphenylgroup, a 2-methyl-6-ethylphenyl group, etc.), an aromatic hydrocarbongroup having a alicyclic hydrocarbon group (a p-cycrohexylphenyl group,a p-adamantylphenyl group, etc.) and the like.

When the aromatic hydrocarbon group has a chain hydrocarbon group or analicyclic hydrocarbon group, a chain hydrocarbon group having 1 to 18carbon atoms and an alicyclic hydrocarbon group having 3 to 18 carbonatoms are preferable.

Examples of the aromatic hydrocarbon group in which a hydrogen atom issubstituted with an alkoxy group include a p-methoxyphenyl group and thelike.

Examples of the chain hydrocarbon group in which a hydrogen atom issubstituted with an aromatic hydrocarbon group include aralkyl groupssuch as a benzyl group, a phenethyl group, a phenylpropyl group, atrityl group, a naphthylmethyl group and a naphthylethyl group.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, aheptyloxy group, an octyloxy group, a decyloxy group and a dodecyloxygroup.

Examples of the alkylcarbonyl group include an acetyl group, a propionylgroup and a butyryl group.

Examples of the halogen atom include a fluorine atom, a chlorine atom, abromine atom and an iodine atom.

Examples of the alkylcarbonyloxy group include a methylcarbonyloxygroup, an ethylcarbonyloxy group, a propylcarbonyloxy group, anisopropylcarbonyloxy group, a butylcarbonyloxy group, asec-butylcarbonyloxy group, a tert-butylcarbonyloxy group, apentylcarbonyloxy group, a hexylcarbonyloxy group, an octylcarbonyloxygroup and a 2-ethylhexylcarbonyloxy group.

The ring formed by bonding R^(b4) and R^(b5) each other, together withsulfur atoms to which R^(b4) and R^(b5) are bonded, may be a monocyclic,polycyclic, aromatic, nonaromatic, saturated or unsaturated ring. Thisring includes a ring having 3 to 18 carbon atoms and is preferably aring having 4 to 18 carbon atoms. The ring containing a sulfur atomincludes a 3-membered to 12-membered ring and is preferably a 3-memberedto 7-membered ring and includes, for example, the following rings andthe like. * represents a bonding site.

The ring formed by combining R^(b9) and R^(b10) together may be amonocyclic, polycyclic, aromatic, nonaromatic, saturated or unsaturatedring. This ring includes a 3-membered to 12-membered ring and ispreferably a 3-membered to 7-membered ring. The ring includes, forexample, a thiolan-1-ium ring (tetrahydrothiophenium ring), athian-1-ium ring, a 1,4-oxathian-4-ium ring and the like.

The ring formed by combining R^(b11) and R^(b12) together may be amonocyclic, polycyclic, aromatic, nonaromatic, saturated or unsaturatedring. This ring includes a 3-membered to 12-membered ring and ispreferably a 3-membered to 7-membered ring. Examples thereof include anoxocycloheptane ring, an oxocyclohexane ring, an oxonorbornane ring, anoxoadamantane ring and the like.

Among cation (b2-1) to cation (b2-4), a cation (b2-1) is preferred.

Examples of the cation (b2-1) include the following cations and thelike.

Examples of the cation (b2-2) include the following cations and thelike.

Examples of the cation (b2-3) include the following cations and thelike.

Examples of the cation (b2-4) include the following cations and thelike.

The acid generator (B) is a combination of the sulfonic acid anionmentioned above and the organic cation mentioned above, and these can beoptionally combined. The acid generator (B) preferably includes acombination of an anion represented by any one of formula (B1a-1) toformula (B1a-3) and formula (B1a-7) to formula (B1a-16), formula(B1a-18), formula (B1a-19) and formula (B1a-22) to formula (B1a-34) witha cation (b2-1) or a cation (b2-3).

The acid generator (B) preferably includes those represented by formula(B1-1) to formula (B1-48). Among these acid generators, those containingan arylsulfonium cation are preferred and those represented by formula(B1-1) to formula (B1-3), formula (B1-5) to formula (B1-7), formula(B1-11) to formula (B1-14), formula (B1-20) to formula (B1-26), formula(B1-29) and formula (B1-31) to formula (B1-48) are particularlypreferred.

When the salt (I) and the acid generator (B) are included as the acidgenerator, a ratio of the content of the salt (I) and that of the acidgenerator (B) (mass ratio; salt (I):acid generator (B)) is usually 1:99to 99:1, preferably 2:98 to 98:2, more preferably 5:95 to 95:5, stillmore preferably 10:90 to 90:10, and particularly preferably 15:85 to85:15.

<Resist Composition>

The resist composition of the present invention includes an acidgenerator including a salt (I) and a resin having an acid-labile group(hereinafter sometimes referred to as “resin (A)”). The “acid-labilegroup” means a group having a leaving group which is eliminated bycontact with an acid, thus converting a constitutional unit into aconstitutional unit having a hydrophilic group (e.g. a hydroxy group ora carboxy group).

The resist composition of the present invention preferably includes aquencher such as a salt generating an acid having an acidity lower thanthat of an acid generated from the acid generator (hereinafter sometimesreferred to as “quencher (C)”), and preferably includes a solvent(hereinafter sometimes referred to as “solvent (E)”).

<Acid Generator>

In the resist composition of the present invention, the content of theacid generator is preferably 1 part by mass or more and 40 parts by massor less, more preferably 3 parts by mass or more and 35 parts by mass orless, and still more preferably 10 parts by mass or more and 35 parts bymass or less, based on 100 parts by mass of the below-mentioned resin(A).

<Resin (A)>

The resin (A) includes a structural unit having an acid-labile group(hereinafter sometimes referred to as “structural unit (a1)”). It ispreferred that the resin (A) further includes a structural unit otherthan the structural unit (a1). Examples of the structural unit otherthan the structural unit (a1) include a structural unit having noacid-labile group (hereinafter sometimes referred to as “structural unit(s)”), a structural unit other than the structural unit (a1) and thestructural unit (s) (e.g. a structural unit having a halogen atommentioned later (hereinafter sometimes referred to as “structural unit(a4)”), a structural unit having a non-leaving hydrocarbon groupmentioned later (hereinafter sometimes referred to as “structural unit(a5)) and other structural units derived from monomers known in the art.

<Structural Unit (a1)>

The structural unit (a1) is derived from a monomer having an acid-labilegroup (hereinafter sometimes referred to as “monomer (a1)”).

The acid-labile group contained in the resin (A) is preferably a grouprepresented by formula (1) (hereinafter also referred to as group (1))and/or a group represented by formula (2) (hereinafter also referred toas group (2)):

wherein, in formula (1), R^(a1), R^(a2) and R^(a3) each independentlyrepresent an alkyl group having 1 to 8 carbon atoms, an alicyclichydrocarbon group having 3 to 20 carbon atoms or groups obtained bycombining these groups, or R^(a1) and R^(a2) are bonded to each other toform a nonaromatic hydrocarbon ring having 3 to 20 carbon atoms togetherwith carbon atoms to which R^(a1) and R^(a2) are bonded,

-   -   ma and na each independently represent 0 or 1, and at least one        of ma and na represents 1, and    -   * represents a bonding site:

wherein, in formula (2), R^(a1′) and R^(a2′) each independentlyrepresent a hydrogen atom or a hydrocarbon group having 1 to 12 carbonatoms, R^(a3′) represents a hydrocarbon group having 1 to 20 carbonatoms, or R^(a2′) and R^(a3′) are bonded to each other to form aheterocyclic ring having 3 to 20 carbon atoms together with carbon atomsand X to which R^(a2′) and R^(a3′) are bonded, and —CH₂— included in thehydrocarbon group and the heterocyclic ring may be replaced by —O— or—S—,

-   -   X represents an oxygen atom or a sulfur atom,    -   na′ represents 0 or 1, and    -   * represents a bonding site.

Examples of the alkyl group in R^(a1), R^(a2) and R^(a3) include amethyl group, an ethyl group, a propyl group, a butyl group, a pentylgroup, a hexyl group, a heptyl group, an octyl group and the like.

The alicyclic hydrocarbon group in R^(a1), R^(a2) and R^(a3) may beeither monocyclic or polycyclic. Examples of the monocyclic alicyclichydrocarbon group include cycloalkyl groups such as a cyclopentyl group,a cyclohexyl group, a cycloheptyl group and a cyclooctyl group. Examplesof the polycyclic alicyclic hydrocarbon group include adecahydronaphthyl group, an adamantyl group, a norbornyl group and thefollowing groups (* represents a bonding site). The number of carbonatoms of the alicyclic hydrocarbon group for R^(a1), R^(a2) and R^(a3)is preferably 3 to 16.

The group obtained by combining an alkyl group with an alicyclichydrocarbon group includes, a for example, a methylcyclohexyl group, adimethylcyclohexyl group, a methylnorbornyl group, a cyclohexylmethylgroup, an adamantylmethyl group, an adamantyldimethyl group, anorbornylethyl group and the like.

Preferably, ma is 0 and na is 1.

When R^(a1) and R^(a2) are bonded to each other to form a nonaromatichydrocarbon ring, examples of —C(R^(a1))(R^(a2)) (R^(a) 3) include thefollowing rings. The nonaromatic hydrocarbon ring preferably has 3 to 12carbon atoms. * represents a bonding site to —O—.

Examples of the hydrocarbon group in R^(a1′), R^(a2′) and R^(a3′)include an alkyl group, an alicyclic hydrocarbon group, an aromatichydrocarbon group and groups obtained by combining these groups.

Examples of the alkyl group and the alicyclic hydrocarbon group includethose which are the same as mentioned in R^(a1), R^(a2) and R^(a3).

Examples of the aromatic hydrocarbon group include aryl groups such as aphenyl group, a naphthyl group, an anthryl group, a biphenyl group and aphenanthryl group.

Examples of the group combined include a group obtained by combining theabove-mentioned alkyl group and alicyclic hydrocarbon group (e.g. acycloalkylalkyl group), an aralkyl group such as a benzyl group, anaromatic hydrocarbon group having an alkyl group (a p-methylphenylgroup, a p-tert-butylphenyl group, a tolyl group, a xylyl group, acumenyl group, a mesityl group, a 2,6-diethylphenyl group, a2-methyl-6-ethylphenyl group, etc.), an aromatic hydrocarbon grouphaving an alicyclic hydrocarbon group (a p-cyclohexylphenyl group, ap-adamantylphenyl group, etc.), an aryl-cycloalkyl group such as aphenylcyclohexyl group, and the like.

When R^(a2′) and R^(a3′) are bonded to each other to form a heterocyclicring together with carbon atoms and X to which R^(a2′) and R^(a3′) arebonded, examples of —C(R^(a1′)) (R^(a3′))—X—R^(a2′) include thefollowing rings. * represents a bonding site.

Among R^(a1′) and R^(a2′), at least one is preferably a hydrogen atom.

-   -   na′ is preferably 0.

Examples of the group (1) include the following groups.

A group wherein, in formula (1), R^(a1), R^(a2) and R^(a3) are alkylgroups, ma=0 and na=1. The group is preferably a tert-butoxycarbonylgroup.

A group wherein, in formula (1), R^(a1) and R^(a2) are bonded to eachother to form an adamantyl group together with carbon atoms to whichR^(a1) and R^(a2) are bonded, R^(a3) is an alkyl group, ma=0 and na=1.

A group wherein, in formula (1), R^(a1) and R^(a2) are eachindependently an alkyl group, R^(a3) is an adamantyl group, ma=0 andna=1.

Specific examples of the group (1) include the following groups. *represents a bonding site.

Specific examples of the group (2) include the following groups. *represents a bonding site.

The monomer (a1) is preferably a monomer having an acid-labile group andan ethylenic unsaturated bond, and more preferably a (meth)acrylicmonomer having an acid-labile group.

Among the (meth)acrylic monomers having an acid-labile group, thosehaving an alicyclic hydrocarbon group having 5 to 20 carbon atoms arepreferably exemplified. When a resin (A) including a structural unitderived from a monomer (a1) having a bulky structure such as analicyclic hydrocarbon group is used in a resist composition, it ispossible to improve the resolution of a resist pattern.

The structural unit derived from a (meth)acrylic monomer having a group(1) includes a structural unit represented by formula (a1-0)(hereinafter sometimes referred to as structural unit (a1-0)), astructural unit represented by formula (a1-1) (hereinafter sometimesreferred to as structural unit (a1-1)) or a structural unit representedby formula (a1-2) (hereinafter sometimes referred to as structural unit(a1-2)). These structural units may be used alone, or two or morestructural units may be used in combination. A structural unit (a1-1)and/or structural unit (a1-2) is preferable.

In formula (a1-0), formula (a1-1) and formula (a1-2),

-   -   L^(a01), L^(a1) and L^(a2) each independently represent —O— or        *—O—(CH₂)_(k1)—CO—O—, k1 represents an integer of 1 to 7, and *        represents a bonding site to —CO—,    -   R^(a01), R^(a4) and R^(a5) each independently represent a        hydrogen atom or a methyl group,    -   R^(a02), R^(a03) and R^(a04) each independently represent an        alkyl group having 1 to 8 carbon atoms, an alicyclic hydrocarbon        group having 3 to 18 carbon atoms or groups obtained by        combining these groups,    -   R^(a6) and R^(a7) each independently represent an alkyl group        having 1 to 8 carbon atoms, an alicyclic hydrocarbon group        having 3 to 18 carbon atoms or groups obtained by combining        these groups,    -   m1 represents an integer of 0 to 14,    -   n1 represents an integer of 0 to 10, and    -   n1′ represents an integer of 0 to 3.    -   R^(a01), R^(a4) and R^(a5) are preferably a methyl group.    -   L^(a01), L^(a1) and L^(a2) are preferably an oxygen atom or        *—O—(CH₂)_(k01)—CO—O— (in which k01 is preferably an integer of        1 to 4, and more preferably 1), and more preferably an oxygen        atom.

Examples of the alkyl group, the alicyclic hydrocarbon group and groupsobtained by combining these groups in R^(a02), R^(a03), R^(a04), R^(a6)and R^(a7) include the same groups as mentioned for R^(a1), R^(a2) andR^(a3) of formula (1).

The number of the carbon atoms of the alkyl group in R^(a02), R^(a03),and R^(a04) is preferably 1 to 6, more preferably a methyl group or anethyl group, and still more preferably a methyl group.

The number of the carbon atoms of the alkyl group in R^(a6) and R^(a7)is preferably 1 to 6, more preferably a methyl group, an ethyl group oran isopropyl group, and still more preferably an ethyl group or anisopropyl group.

The number of carbon atoms of the alicyclic hydrocarbon group ofR^(a02), R^(a03), R^(a04), R^(a6) and R^(a7) is preferably 5 to 12, andmore preferably 5 to 10.

The total number of carbon atoms of the group obtained by combining thealkyl group with the alicyclic hydrocarbon group is preferably 18 orless.

R^(a02) and R^(a03) are preferably an alkyl group having 1 to 6 carbonatoms, and more preferably a methyl group or an ethyl group.

R^(a04) is preferably an alkyl group having 1 to 6 carbon atoms or analicyclic hydrocarbon group having 5 to 12 carbon atoms, and morepreferably a methyl group, an ethyl group, a cyclohexyl group or anadamantyl group.

Preferably, R^(a6) and R^(a7) are each independently an alkyl grouphaving 1 to 6 carbon atoms, more preferably a methyl group, an ethylgroup or an isopropyl group, and still more preferably an ethyl group oran isopropyl group.

-   -   m1 is preferably an integer of 0 to 3, and more preferably 0 or        1.    -   n1 is preferably an integer of 0 to 3, and more preferably 0 or        1.    -   n1′ is preferably 0 or 1.

The structural unit (a1-0) includes, for example, a structural unitrepresented by any one of formula (a1-0-1) to formula (a1-0-12) and astructural unit in which a methyl group corresponding to R^(a01) in thestructural unit (a1-0) is substituted with a hydrogen atom and ispreferably a structural unit represented by any one of formula (a1-0-1)to formula (a1-0-10).

The structural unit (a1-1) includes, for example, structural unitsderived from the monomers mentioned in JP 2010-204646 A. Among thesestructural units, a structural unit represented by any one of formula(a1-1-1) to formula (a1-1-4) and a structural unit in which a methylgroup corresponding to R^(a4) in the structural unit (a1-1) issubstituted with a hydrogen atom are preferred, and a structural unitrepresented by any one of formula (a1-1-1) to formula (a1-1-4) is morepreferred.

Examples of the structural unit (a1-2) include a structural unitrepresented by any one of formula (a1-2-1) to formula (a1-2-6) and astructural unit in which a methyl group corresponding to R^(a5) in thestructural unit (a1-2) is substituted with a hydrogen atom, andstructural units represented by formula (a1-2-2), formula (a1-2-5) andformula (a1-2-6) are preferred.

When the resin (A) includes a structural unit (a1-0), the contentthereof is usually 5 to 60 mol %, preferably 5 to 50 mol %, morepreferably 10 to 40 mol %, based on all structural units of the resin(A).

When the resin (A) includes a structural unit (a1-0) and/or a structuralunit (a1-1) and/or a structural unit (a1-2), the total content thereofis usually 10 to 95 mol %, preferably 15 to 90 mol %, more preferably 20to 85 mol %, still more preferably 25 to 80 mol %, and yet morepreferably 30 to 75 mol %, based on all structural units of the resin(A).

In the structural unit (a1), examples of the structural unit having agroup (2) include a structural unit represented by formula (a1-4)(hereinafter sometimes referred to as “structural unit (a1-4)”):

wherein, in formula (a1-4),

-   -   R^(a32) represents a hydrogen atom, a halogen atom or an alkyl        group having 1 to 6 carbon atoms optionally having a halogen        atom,    -   R^(a33) represents a halogen atom, a hydroxy group, an alkyl        group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6        carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms,        an alkylcarbonyloxy group having 2 to 4 carbon atoms, an        acryloyloxy group or a methacryloyloxy group.    -   la represents an integer of 0 to 4, and when la is 2 or more, a        plurality of R^(a33) may be the same or different from each        other, and    -   R^(a34) and R^(a35) each independently represent a hydrogen atom        or a hydrocarbon group having 1 to 12 carbon atoms, R^(a36)        represents a hydrocarbon group having 1 to 20 carbon atoms, or        R^(a35) and R^(a36) are bonded to each other to form a divalent        hydrocarbon group having 2 to 20 carbon atoms together with        —C—O— to which R^(a35) and R^(a36) are bonded, and —CH₂—        included in the hydrocarbon group and the divalent hydrocarbon        group may be replaced by —O— or —S—.

Examples of the alkyl group in R^(a32) and R^(a33) include a methylgroup, an ethyl group, a propyl group, an isopropyl group, a butylgroup, a pentyl group and a hexyl group. The alkyl group is preferablyan alkyl group having 1 to 4 carbon atoms, more preferably a methylgroup or an ethyl group, and still more preferably a methyl group.

Examples of the halogen atom in R^(a32) and R^(a33) include a fluorineatom, a chlorine atom and a bromine atom.

Examples of the alkyl group having 1 to 6 carbon atoms optionally havinga halogen atom include a trifluoromethyl group, a difluoromethyl group,a methyl group, a perfluoroethyl group, a 2,2,2-trifluoroethyl group, a1,1,2,2-tetrafluoroethyl group, an ethyl group, a perfluoropropyl group,a 2,2,3,3,3-pentafluoropropyl group, a propyl group, a perfluorobutylgroup, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a butyl group, aperfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, apentyl group, a hexyl group, a perfluorohexyl group and the like.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropoxy group, a butoxy group, a pentyloxy group and a hexyloxy group.Among these groups, an alkoxy group having 1 to 4 carbon atoms ispreferred, a methoxy group or an ethoxy group are more preferred, and amethoxy group is still more preferred.

Examples of the alkylcarbonyl group include an acetyl group, a propionylgroup and a butyryl group.

Examples of the alkylcarbonyloxy group include an acetyloxy group, apropionyloxy group, a butyryloxy group and the like.

Examples of the hydrocarbon group in R^(a34), R^(a35) and R^(a36)include an alkyl group, an alicyclic hydrocarbon group, an aromatichydrocarbon group and groups obtained by combining these groups.

Examples of the alkyl group include a methyl group, an ethyl group, apropyl group, a butyl group, a pentyl group, a hexyl group, a heptylgroup, an octyl group and the like.

The alicyclic hydrocarbon group may be either monocyclic or polycyclic,and examples of the monocyclic alicyclic hydrocarbon group includecycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, acycloheptyl group and a cyclooctyl group. Examples of the polycyclicalicyclic hydrocarbon group include a decahydronaphthyl group, anadamantyl group, a norbornyl group and the following groups (*represents a bonding site).

Examples of the aromatic hydrocarbon group include aryl groups such as aphenyl group, a naphthyl group, an anthryl group, a biphenyl group and aphenanthryl group.

Examples of the combined group include a group obtained by combining theabove-mentioned alkyl group and alicyclic hydrocarbon group (e.g. acycloalkylalkyl group), an aralkyl group such as a benzyl group, anaromatic hydrocarbon group having an alkyl group (a p-methylphenylgroup, a p-tert-butylphenyl group, a tolyl group, a xylyl group, acumenyl group, a mesityl group, a 2,6-diethylphenyl group, a2-methyl-6-ethylphenyl group, etc.), an aromatic hydrocarbon grouphaving an alicyclic hydrocarbon group (a p-cyclohexylphenyl group, ap-adamantylphenyl group, etc.), an aryl-cyclohexyl group such as aphenylcyclohexyl group and the like. Particularly, examples of R^(a36)include an alkyl group having 1 to 18 carbon atoms, an alicyclichydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbongroup having 6 to 18 carbon atoms or groups obtained by combining thesegroups.

In formula (a1-4), R^(a32) is preferably a hydrogen atom,

-   -   R^(a33) is preferably an alkoxy group having 1 to 4 carbon        atoms, more preferably a methoxy group and an ethoxy group, and        still more preferably a methoxy group,    -   la is preferably 0 or 1, and more preferably 0,    -   R^(a34) is preferably a hydrogen atom, and    -   R^(a35) is preferably an alkyl group having 1 to 12 carbon atoms        or an alicyclic hydrocarbon group, and more preferably a methyl        group or an ethyl group.

The hydrocarbon group for R^(a36) is preferably an alkyl group having 1to 18 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbonatoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms orgroups formed by combining these groups, and more preferably an alkylgroup having 1 to 18 carbon atoms, an alicyclic aliphatic hydrocarbongroup having 3 to 18 carbon atoms or an aralkyl group having 7 to 18carbon atoms. The alkyl group and the alicyclic hydrocarbon group inR^(a36) are preferably unsubstituted. The aromatic hydrocarbon group inR^(a36) is preferably an aromatic ring having an aryloxy group having 6to 10 carbon atoms.

—OC(R^(a34)) (R^(a35))—O—R^(a36) in the structural unit (a1-4) iseliminated by contacting with an acid (e.g., p-toluenesulfonic acid) toform a hydroxy group.

The structural unit (a1-4) includes, for example, structural unitsderived from the monomers mentioned in JP 2010-204646 A. The structuralunit preferably includes structural units represented by formula(a1-4-1) to formula (a1-4-12) and a structural unit in which a hydrogenatom corresponding to R^(a32) in the constitutional unit (a1-4) issubstituted with a methyl group, and more preferably structural unitsrepresented by formula (a1-4-1) to formula (a1-4-5) and formula(a1-4-10).

When the resin (A) includes the structural unit (a1-4), the content ispreferably 10 to 95 mol %, more preferably 15 to 90 mol %, still morepreferably 20 to 85 mol %, yet more preferably 20 to 70 mol %, andparticularly preferably 20 to 60 mol %, based on the total of allstructural units of the resin (A).

The structural unit derived from a (meth)acrylic monomer having a group(2) also includes a structural unit represented by formula (a1-5)(hereinafter sometimes referred to as “structural unit (a1-5)”).

In formula (a1-5),

-   -   R^(a8) represents an alkyl group having 1 to 6 carbon atoms        optionally having a halogen atom, a hydrogen atom or a halogen        atom,    -   Z^(a1) represents a single bond or *—(CH₂)_(b3)—CO-L⁵⁴-, h3        represents an integer of 1 to 4, and * represents a bonding site        to L⁵¹,    -   L⁵¹, L⁵², L⁵³ and L⁵⁴ each independently represent —O— or —S—,    -   s1 represents an integer of 1 to 3, and    -   s1′ represents an integer of 0 to 3.

The halogen atom includes a fluorine atom and a chlorine atom and ispreferably a fluorine atom. Examples of the alkyl group having 1 to 6carbon atoms optionally having a halogen atom include a methyl group, anethyl group, a propyl group, a butyl group, a pentyl group, a hexylgroup, a heptyl group, an octyl group, a fluoromethyl group and atrifluoromethyl group.

In formula (a1-5), R^(a8) is preferably a hydrogen atom, a methyl groupor a trifluoromethyl group,

-   -   L⁵¹ is preferably an oxygen atom,    -   one of L⁵² and L⁵³ is preferably —O— and the other one is        preferably —S—,    -   s1 is preferably 1,    -   s1′ is preferably an integer of 0 to 2, and    -   Z^(a1) is preferably a single bond or *—CH₂—CO—O—.

The structural unit (a1-5) includes, for example, structural unitsderived from the monomers mentioned in JP 2010-61117 A. Among thesestructural units, structural units represented by formula (a1-5-1) toformula (a1-5-4) are preferred, and structural units represented byformula (a1-5-1) or formula (a1-5-2) are more preferred.

When the resin (A) includes the structural unit (a1-5), the content ispreferably 1 to 50 mol %, more preferably 3 to 45 mol %, still morepreferably 5 to 40 mol %, and yet more preferably 5 to 30 mol %, basedon all structural units of the resin (A).

The structural unit (a1) also includes the following structural units.

When the resin (A) includes the above-mentioned structural units such as(a1-3-1) to (a1-3-7), the content is preferably 10 to 95 mol %, morepreferably 15 to 90 mol %, still more preferably 20 to 85 mol %, yetmore preferably 20 to 70 mol %, and particularly preferably 20 to 60 mol%, based on all structural units of the resin (A).

<Structural Unit (s)>

The structural unit (s) is derived from a monomer having no acid-labilegroup (hereinafter sometimes referred to as “monomer (s)”). It ispossible to use, as the monomer from which the structural unit (s) isderived, a monomer having no acid-labile group known in the resistfield.

The structural unit (s) preferably has a hydroxy group or a lactonering. When a resin including a structural unit having a hydroxy groupand having no acid-labile group (hereinafter sometimes referred to as“structural unit (a2)”) and/or a structural unit having a lactone ringand having no acid-labile group (hereinafter sometimes referred to as“structural unit (a3)”) is used in the resist composition of the presentinvention, it is possible to improve the resolution of a resist patternand the adhesion to a substrate.

<Structural Unit (a2)>

The hydroxy group possessed by the structural unit (a2) may be either analcoholic hydroxy group or a phenolic hydroxy group.

When a resist pattern is produced from the resist composition of thepresent invention, in the case of using, as an exposure source, highenergy rays such as KrF excimer laser (248 nm), electron beam or extremeultraviolet light (EUV), it is preferred to use a structural unit (a2)having a phenolic hydroxy group as the structural unit (a2). When usingArF excimer laser (193 nm) or the like, a structural unit (a2) having analcoholic hydroxy group is preferably used as the structural unit (a2),and it is more preferably use a structural unit (a2-1) mentioned later.The structural unit (a2) may be included alone, or two or morestructural units may be included.

In the structural unit (a2), examples of the structural unit having aphenolic hydroxy group include a structural unit represented by formula(a2-A) (hereinafter sometimes referred to as “structural unit (a2-A)”):

wherein, in formula (a2-A),

-   -   R^(a50) represents a hydrogen atom, a halogen atom or an alkyl        group having 1 to 6 carbon atoms optionally having a halogen        atom,    -   R^(a51) represents a halogen atom, a hydroxy group, an alkyl        group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6        carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms,        an alkylcarbonyloxy group having 2 to 4 carbon atoms, an        acryloyloxy group or a methacryloyloxy group,    -   A^(a50) represents a single bond or        *—X^(a51)-(A^(a52)-X^(a52))_(nb)—, and * represents a bonding        site to carbon atoms to which —R^(a50) is bonded,    -   A^(a52) each independently represent an alkanediyl group having        1 to 6 carbon atoms,    -   X^(a51) and X^(a52) each independently represent —O—, —CO—O— or        —O—CO—,    -   nb represents 0 or 1, and    -   mb represents an integer of 0 to 4, and when mb is an integer of        2 or more, a plurality of R^(a51) may be the same or different        from each other.

Examples of the halogen atom in R^(a50) include a fluorine atom, achlorine atom and a bromine atom.

Examples of the alkyl group having 1 to 6 carbon atoms optionally havinga halogen atom in R^(a50) include a trifluoromethyl group, adifluoromethyl group, a methyl group, a perfluoroethyl group, a2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethylgroup, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, apropyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutylgroup, a butyl group, a perfluoropentyl group, a2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl groupand a perfluorohexyl group.

R^(a50) is preferably a hydrogen atom or an alkyl group having 1 to 4carbon atoms, more preferably a hydrogen atom, a methyl group or anethyl group, and still more preferably a hydrogen atom or a methylgroup.

Examples of the alkyl group in R^(a51) include a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, a sec-butylgroup, a tert-butyl group, a pentyl group and a hexyl group.

Examples of the alkoxy group in R^(a51) include a methoxy group, anethoxy group, a propoxy group, an isopropoxy group, a butoxy group, asec-butoxy group and a tert-butoxy group. An alkoxy group having 1 to 4carbon atoms is preferred, a methoxy group or an ethoxy group is morepreferred, and a methoxy group is still more preferred.

Examples of the alkylcarbonyl group in R^(a51) include an acetyl group,a propionyl group and a butyryl group.

Examples of the alkylcarbonyloxy group in R^(a51) include an acetyloxygroup, a propionyloxy group and a butyryloxy group.

R^(a51) is preferably a methyl group.

Examples of *—X^(a51)-(A^(a52)-X^(a52))_(nb)— include *—O—, *—CO—O—,*—O—CO—, *—CO—O-A^(a52)-CO—O—, *—O—CO-A^(a52)-O—, *—O-A^(a52)-CO—O—,*—CO-A^(a52)-CO— and *—O—CO-A^(a52)-O—CO—. Among these, *—CO—O—,*—CO—O-A^(a52)-CO—O— or *—O-A^(a52)-CO—O— is preferred.

Examples of the alkanediyl group include a methylene group, an ethylenegroup, a propane-1,3-diyl group, a propane-1,2-diyl group, abutane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diylgroup, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group and a2-methylbutane-1,4-diyl group.

-   -   A⁵² is preferably a methylene group or an ethylene group.    -   A^(a50) is preferably a single bond, *—CO—O— or        *—CO—O-A^(a52)-CO—O—, more preferably a single bond, *—CO—O— or        *—CO—O—CH₂—CO—O—, and still more preferably a single bond or        *—CO—O—.    -   mb is preferably 0, 1 or 2, more preferably 0 or 1, and        particularly preferably 0.

The hydroxy group is preferably bonded to the o-position or thep-position of a benzene ring, and more preferably the p-position.

Examples of the structural unit (a2-A) include structural units derivedfrom the monomers mentioned in JP 2010-204634 A and JP 2012-12577 A.

Examples of the structural unit (a2-A) include structural unitsrepresented by formula (a2-2-1) to formula (a2-2-6), and a structuralunit in which a methyl group corresponding to R^(a50) in the structuralunit (a2-A) is substituted with a hydrogen atom in structural unitsrepresented by formula (a2-2-1) to formula (a2-2-6). The structural unit(a2-A) is preferably a structural unit in which a methyl groupcorresponding to R^(a50) in the structural unit (a2-A) is substitutedwith a hydrogen atom in the structural unit represented by formula(a2-2-1), the structural unit represented formula (a2-2-3), thestructural unit represented by formula (a2-2-6) and the structural unitrepresented by formula (a2-2-1), the structural unit represented byformula (a2-2-3) or the structural unit represented by formula (a2-2-6).

When the structural unit (a2-A) is included in the resin (A), thecontent of the structural unit (a2-A) is preferably 5 to 80 mol %, morepreferably 10 to 70 mol %, still more preferably 15 to 65 mol %, and yetmore preferably 20 to 65 mol %, based on all structural units.

The structural unit (a2-A) can be included in a resin (A) bypolymerizing, for example, with a structural unit (a1-4) and treatingwith an acid such as p-toluenesulfonic acid. The structural unit (a2-A)can also be included in the resin (A) by polymerizing withacetoxystyrene and treating with an alkali such as tetramethylammoniumhydroxide.

Examples of the structural unit having an alcoholic hydroxy group in thestructural unit (a2) include a structural unit represented by formula(a2-1) (hereinafter sometimes referred to as “structural unit (a2-1)”).

In formula (a2-1),

-   -   L^(a3) represents —O— or *—O—(CH₂)_(k2)—CO—O—,    -   k2 represents an integer of 1 to 7, and * represents a bonding        site to —CO—,    -   R^(a14) represents a hydrogen atom or a methyl group,    -   R^(a15) and R^(a16) each independently represent a hydrogen        atom, a methyl group or a hydroxy group, and    -   o1 represents an integer of 0 to 10.

In formula (a2-1), L^(a3) is preferably —O— or —O—(CH₂)_(f1)—CO—O— (f1represents an integer of 1 to 4), and more preferably —O—,

-   -   R^(a14) is preferably a methyl group,    -   R^(a15) is preferably a hydrogen atom,    -   R^(a16) is preferably a hydrogen atom or a hydroxy group, and    -   o1 is preferably an integer of 0 to 3, and more preferably 0 or        1.

The structural unit (a2-1) includes, for example, structural unitsderived from the monomers mentioned in JP 2010-204646 A. A structuralunit represented by any one of formula (a2-1-1) to formula (a2-1-6) ispreferred, a structural unit represented by any one of formula (a2-1-1)to formula (a2-1-4) is more preferred, and a structural unit representedby formula (a2-1-1) or formula (a2-1-3) is still more preferred.

When the resin (A) includes the structural unit (a2-1), the content isusually 1 to 45 mol %, preferably 1 to 40 mol %, more preferably 1 to 35mol %, and still more preferably 2 to 20 mol %, based on all structuralunits of the resin (A).

<Structural Unit (a3)>

The lactone ring possessed by the structural unit (a3) may be amonocyclic ring such as a β-propiolactone ring, a γ-butyrolactone ringor a δ-valerolactone ring, or a condensed ring of a monocyclic lactonering and the other ring. Preferably, a γ-butyrolactone ring, anadamantanelactone ring or a bridged ring including a γ-butyrolactonering structure (e.g. a structural unit represented by the followingformula (a3-2)) is exemplified.

The structural unit (a3) is preferably a structural unit represented byformula (a3-1), formula (a3-2), formula (a3-3) or formula (a3-4). Thesestructural units may be included alone, or two or more structural unitsmay be included:

wherein, in formula (a3-1), formula (a3-2), formula (a3-3) and formula(a3-4),

-   -   L^(a4), L^(a5) and L^(a6) each independently represent —O— or a        group represented by *—O—(CH₂)_(k3)—CO— (k3 represents an        integer of 1 to 7),    -   L^(a7) represents —O—, *—O-L^(a8)-O—, *—O-L^(a8)-CO—O—,        *—O-L^(a8)-CO—O-L^(a9)-CO—O— or *—O-L^(a8)-O—CO-L^(a9)-O—,    -   L^(a8) and L^(a9) each independently represent an alkanediyl        group having 1 to 6 carbon atoms,    -   * represents a bonding site to a carbonyl group,    -   R^(a18), R^(a19) and R^(a20) each independently represent a        hydrogen atom or a methyl group,    -   R^(a24) represents an alkyl group having 1 to 6 carbon atoms        optionally having a halogen atom, a hydrogen atom or a halogen        atom,    -   X^(a3) represents —CH₂— or an oxygen atom,    -   R^(a21) represents an aliphatic hydrocarbon group having 1 to 4        carbon atoms,    -   R^(a22), R^(a23) and R^(a24) each independently represent a        carboxy group, a cyano group or an aliphatic hydrocarbon group        having 1 to 4 carbon atoms,    -   p1 represents an integer of 0 to 5,    -   q1 represents an integer of 0 to 3,    -   r1 represents an integer of 0 to 3,    -   w1 represents an integer of 0 to 8, and    -   when p1, q1, r1 and/or w1 is/are 2 or more, a plurality of        R^(a21), R^(a22), R^(a23) and/or R^(a25) may be the same or        different from each other.

Examples of the aliphatic hydrocarbon group in R^(a21), R^(a22), R^(a23)and R^(a25) include alkyl groups such as a methyl group, an ethyl group,a propyl group, an isopropyl group, a butyl group, a sec-butyl group anda tert-butyl group.

Examples of the halogen atom in R^(a24) include a fluorine atom, achlorine atom, a bromine atom and an iodine atom.

Examples of the alkyl group in R^(a24) include a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, a sec-butylgroup, a tert-butyl group, a pentyl group and a hexyl group, and thealkyl group is preferably an alkyl group having 1 to 4 carbon atoms, andmore preferably a methyl group or an ethyl group.

Examples of the alkyl group having a halogen atom in R^(a24) include atrifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group,a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butylgroup, a perfluorotert-butyl group, a perfluoropentyl group, aperfluorohexyl group, a trichloromethyl group, a tribromomethyl group, atriiodomethyl group and the like.

Examples of the alkanediyl group in L^(a8) and L^(a9) include amethylene group, an ethylene group, a propane-1,3-diyl group, apropane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diylgroup, a hexane-1,6-diyl group, a butane-1,3-diyl group, a2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, apentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group.

In formula (a3-1) to formula (a3-3), preferably, L^(a4) to L^(a6) areeach independently —O— or a group in which k3 is an integer of 1 to 4 in*—O—(CH₂)_(k3)—CO—, more preferably —O— and *—O—CH₂—CO—O—, and stillmore preferably an oxygen atom,

-   -   R^(a18) to R^(a21) are preferably a methyl group,    -   preferably, R^(a22) and R^(a23) are each independently a carboxy        group, a cyano group or a methyl group, and    -   preferably, p1, q1 and r1 are each independently an integer of 0        to 2, and more preferably 0 or 1.

In formula (a3-4), R^(a24) is preferably a hydrogen atom or an alkylgroup having 1 to 4 carbon atoms, more preferably a hydrogen atom, amethyl group or an ethyl group, and still more preferably a hydrogenatom or a methyl group,

-   -   R^(a25) is preferably a carboxy group, a cyano group or a methyl        group,    -   L^(a7) is preferably —O— or *—O-L^(a8)-CO—, and more preferably        —O—, —O—CH₂—CO—O— or —O—C₂H₄—CO—O—, and    -   w1 is preferably an integer of 0 to 2, and more preferably 0 or        1.

Particularly, formula (a3-4) is preferably formula (a3-4)′:

wherein R^(a24) and L^(a7) are the same as defined above.

Examples of the structural unit (a3) include structural units derivedfrom the monomers mentioned in JP 2010-204646 A, the monomers mentionedin JP 2000-122294 A and the monomers mentioned in JP 2012-41274 A. Thestructural unit (a3) is preferably a structural unit represented by anyone of formula (a3-1-1), formula (a3-1-2), formula (a3-2-1), formula(a3-2-2), formula (a3-3-1), formula (a3-3-2) and formula (a3-4-1) toformula (a3-4-12), and structural units in which methyl groupscorresponding to R^(a18), R^(a19), R^(a20) and R^(a24) in formula (a3-1)to formula (a3-4) are substituted with hydrogen atoms in the abovestructural units.

When the resin (A) includes the structural unit (a3), the total contentis usually 5 to 70 mol %, preferably 10 to 65 mol %, and more preferably10 to 60 mol %, based on all structural units of the resin (A).

Each content of the structural unit (a3-1), the structural unit (a3-2),the structural unit (a3-3) or the structural unit (a3-4) is preferably 5to 60 mol %, more preferably 5 to 50 mol %, and still more preferably 10to 50 mol %, based on all structural units of the resin (A).

<Structural Unit (a4)>

Examples of the structural unit (a4) include the following structuralunits:

wherein, in formula (a4),

-   -   R⁴¹ represents a hydrogen atom or a methyl group, and    -   R⁴² represents a saturated hydrocarbon group having 1 to 24        carbon atoms which has a fluorine atom, and —CH₂— included in        the saturated hydrocarbon group may be replaced by —O— or —CO.

Examples of the saturated hydrocarbon group represented by R⁴² include achain saturated hydrocarbon group and a monocyclic or polycyclicalicyclic saturated hydrocarbon group, and groups formed by combiningthese groups.

Examples of the chain saturated hydrocarbon group include a methylgroup, an ethyl group, a propyl group, a butyl group, a pentyl group, ahexyl group, a heptyl group, an octyl group, a decyl group, a dodecylgroup, a pentadecyl group, a hexadecyl group, a heptadecyl group and anoctadecyl group.

Examples of the monocyclic or polycyclic alicyclic saturated hydrocarbongroup include cycloalkyl groups such as a cyclopentyl group, acyclohexyl group, a cycloheptyl group and a cyclooctyl group; andpolycyclic alicyclic saturated hydrocarbon groups such as adecahydronaphthyl group, an adamantyl group, a norbornyl group and thefollowing groups (* represents a bonding site).

Examples of the group formed by combination include groups formed bycombining one or more alkyl groups or one or more alkanediyl groups withone or more alicyclic saturated hydrocarbon groups, and include analkanediyl group-alicyclic saturated hydrocarbon group, an alicyclicsaturated hydrocarbon group-alkyl group, an alkanediyl group-alicyclicsaturated hydrocarbon group-alkyl group and the like.

Examples of the structural unit (a4) include a structural unitrepresented by formula (a4-0), a structural unit represented by formula(a4-1) and a structural unit represented by formula (a4-4):

wherein, in formula (a4-0),

-   -   R⁵⁴ represents a hydrogen atom or a methyl group,    -   L^(4a) represents a single bond or an alkanediyl group having 1        to 4 carbon atoms,    -   L^(3a) represents a perfluoroalkanediyl group having 1 to 8        carbon atoms or a perfluorocycloalkanediyl group having 3 to 12        carbon atoms, and    -   R⁶⁴ represents a hydrogen atom or a fluorine atom.

Examples of the alkanediyl group in L^(4a) include linear alkanediylgroups such as a methylene group, an ethylene group, a propane-1,3-diylgroup and a butane-1,4-diyl group; and branched alkanediyl groups suchas an ethane-1,1-diyl group, a propane-1,2-diyl group, a butane-1,3-diylgroup, a 2-methylpropane-1,3-diyl group and a 2-methylpropane-1,2-diylgroup.

Examples of the perfluoroalkanediyl group in L^(3a) include adifluoromethylene group, a perfluoroethylene group, aperfluoroethylfluoromethylene group, a perfluoropropane-1,3-diyl group,a perfluoropropane-1,2-diyl group, a perfluoropropane-2,2-diyl group, aperfluorobutane-1,4-diyl group, a perfluorobutane-2,2-diyl group, aperfluorobutane-1,2-diyl group, a perfluoropentane-1,5-diyl group, aperfluoropentane-2,2-diyl group, a perfluoropentane-3,3-diyl group, aperfluorohexane-1,6-diyl group, a perfluorohexane-2,2-diyl group, aperfluorohexane-3,3-diyl group, a perfluoroheptane-1,7-diyl group, aperfluoroheptane-2,2-diyl group, a perfluoroheptane-3,4-diyl group, aperfluoroheptane-4,4-diyl group, a perfluorooctane-1,8-diyl group, aperfluorooctane-2,2-diyl group, a perfluorooctane-3,3-diyl group, aperfluorooctane-4,4-diyl group and the like.

Examples of the perfluorocycloalkanediyl group in L³ include aperfluorocyclohexanediyl group, a perfluorocyclopentanediyl group, aperfluorocycloheptanediyl group, a perfluoroadamantanediyl group and thelike.

-   -   L^(4a) is preferably a single bond, a methylene group or an        ethylene group, and more preferably a single bond or a methylene        group.    -   L^(3a) is preferably a perfluoroalkanediyl group having 1 to 6        carbon atoms, and more preferably a perfluoroalkanediyl group        having 1 to 3 carbon atoms.

Examples of the structural unit (a4-0) include the following structuralunits, and structural units in which a methyl group corresponding to R⁵⁴in the structural unit (a4-0) in the following structural units issubstituted with a hydrogen atom:

wherein, in formula (a4-1),

-   -   R^(a41) represents a hydrogen atom or a methyl group,    -   R^(a42) represents a hydrocarbon group having 1 to 20 carbon        atoms which may have a substituent, and —CH— included in the        saturated hydrocarbon group may be replaced by —O— or —CO—,    -   A^(a41) represents an alkanediyl group having 1 to 6 carbon        atoms which may have a substituent or a group represented by        formula (a-g1), in which at least one of A^(a41) and R^(a42)        has, as a substituent, a halogen atom (preferably a fluorine        atom):

-   -   [in which, in formula (a-g1),    -   s represents 0 or 1,    -   A^(a42) and A^(a41) each independently represent a divalent        saturated hydrocarbon group having 1 to 5 carbon atoms which may        have a substituent,    -   A^(a43) represents a single bond or a divalent saturated        hydrocarbon group having 1 to 5 carbon atoms which may have a        substituent,    -   X^(a41) and X^(a42) each independently represent —O—, —CO—,        —CO—O— or —O—CO—, in which the total number of carbon atoms of        A^(a42), A^(a43), A^(a44), X^(a41) and X^(a42) is 7 or less],        and    -   * is a bonding site and * at the right side is a bonding site to        —O—CO—R^(a42).

Examples of the saturated hydrocarbon group in R^(a42) include a chainsaturated hydrocarbon group and a monocyclic or a polycyclic saturatedalicyclic hydrocarbon group, and groups formed by combining thesegroups.

Examples of the chain saturated hydrocarbon group include a methylgroup, an ethyl group, a propyl group, a butyl group, a pentyl group, ahexyl group, a heptyl group, an octyl group, a decyl group, a dodecylgroup, a pentadecyl group, a hexadecyl group, a heptadecyl group and anoctadecyl group.

Examples of the monocyclic or polycyclic saturated alicyclic hydrocarbongroup include cycloalkyl groups such as a cyclopentyl group, acyclohexyl group, a cycloheptyl group and a cyclooctyl group; andpolycyclic alicyclic hydrocarbon groups such as a decahydronaphthylgroup, an adamantyl group, a norbornyl group and the following groups (*represents a bonding site).

Examples of the group formed by combination include groups formed bycombining one or more alkyl groups or one or more alkanediyl groups withone or more saturated alicyclic hydrocarbon groups, and include analkanediyl group-saturated alicyclic hydrocarbon group, a saturatedalicyclic hydrocarbon group-alkyl group, an alkanediyl group-saturatedalicyclic hydrocarbon group-alkyl group and the like.

Examples of the substituent optionally possessed by R^(a42) include atleast one selected from the group consisting of a halogen atom and agroup represented by formula (a-g3). Examples of the halogen atominclude a fluorine atom, a chlorine atom, a bromine atom and an iodineatom, and a fluorine atom is preferred:*—X^(a43)-A^(a45)  (a-g3)wherein, in formula (a-g3),

-   -   X^(a43) represents an oxygen atom, a carbonyl group, *—O—CO— or        *—CO—O— (* represents a bonding site to R^(a42)),    -   A^(a45) represents a saturated hydrocarbon group having 1 to 17        carbon atoms optionally having a halogen atom, and    -   * represents a bonding site.    -   In R^(a42)—X^(a43)-A^(a45), when R^(a42) has no halogen atom,        A^(a45) represents a saturated hydrocarbon group having 1 to 17        carbon atoms having at least one halogen atom.

Examples of the saturated hydrocarbon group in A^(a45) include alkylgroups such as a methyl group, an ethyl group, a propyl group, a butylgroup, a pentyl group, a hexyl group, a heptyl group, an octyl group, adecyl group, a dodecyl group, a pentadecyl group, a hexadecyl group, aheptadecyl group and an octadecyl group; monocyclic alicyclichydrocarbon groups such as a cyclopentyl group, a cyclohexyl group, acycloheptyl group and a cyclooctyl group; and polycyclic alicyclichydrocarbon groups such as a decahydronaphthyl group, an adamantylgroup, a norbornyl group and the following groups (* represents abonding site):

Examples of the group formed by combination include a group obtained bycombining one or more alkyl groups or one or more alkanediyl groups withone or more alicyclic hydrocarbon groups, and include an -alkanediylgroup-alicyclic hydrocarbon group, an -alicyclic hydrocarbon group-alkylgroup, an -alkanediyl group-alicyclic hydrocarbon group-alkyl group andthe like.

R^(a42) is preferably a saturated hydrocarbon group optionally having ahalogen atom, and more preferably an alkyl group having a halogen atomand/or a saturated hydrocarbon group having a group represented byformula (a-g3).

When R^(a42) is a saturated hydrocarbon group having a halogen atom, asaturated hydrocarbon group having a fluorine atom is preferred, aperfluoroalkyl group or a perfluorocycloalkyl group is more preferred, aperfluoroalkyl group having 1 to 6 carbon atoms is still more preferred,and a perfluoroalkyl group having 1 to 3 carbon atoms is particularlypreferred. Examples of the perfluoroalkyl group include aperfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group,a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group,a perfluoroheptyl group and a perfluorooctyl group. Examples of theperfluorocycloalkyl group include a perfluorocyclohexyl group and thelike.

When R^(a42) is a saturated hydrocarbon group having a group representedby formula (a-g3), the total number of carbon atoms of R^(a42) ispreferably 15 or less, and more preferably 12 or less, including thenumber of carbon atoms included in the group represented by formula(a-g3). When having the group represented by formula (a-g3) as thesubstituent, the number thereof is preferably 1.

When R^(a42) is a saturated hydrocarbon group having the grouprepresented by formula (a-g3), R^(a42) is still more preferably a grouprepresented by formula (a-g2):*-A^(a46)-X^(a44)-A^(a47)  (a-g2)wherein, in formula (a-g2),

-   -   A^(a46) represents a divalent saturated hydrocarbon group having        1 to 17 carbon atoms optionally having a halogen atom,    -   X^(a44) represents *—O—CO— or *—CO—O— (* represents a bonding        site to A^(a46)),    -   A^(a47) represents a saturated hydrocarbon group having 1 to 17        carbon atoms optionally having a halogen atom,    -   the total number of carbon atoms of A^(a46), A^(a47) and X^(a44)        is 18 or less, and at least one of A^(a46) and A^(a47) has at        least one halogen atom, and    -   * represents a bonding site to a carbonyl group.

The number of carbon atoms of the saturated hydrocarbon group forA^(a46) is preferably 1 to 6, and more preferably 1 to 3.

The number of carbon atoms of the saturated hydrocarbon group forA^(a47) is preferably 4 to 15, and more preferably 5 to 12, and A^(a47)is still more preferably a cyclohexyl group or an adamantyl group.

Preferred structure of the group represented by formula (a-g2) is thefollowing structure (* is a bonding site to a carbonyl group).

Examples of the alkanediyl group in A^(a42) include linear alkanediylgroups such as a methylene group, an ethylene group, a propane-1,3-diylgroup, a butane-1,4-diyl group, a pentane-1,5-diyl group and ahexane-1,6-diyl group; and branched alkanediyl groups such as apropane-1,2-diyl group, a butane-1,3-diyl group, a2-methylpropane-1,2-diyl group, a 1-methylbutane-1,4-diyl group and a2-methylbutane-1,4-diyl group.

Examples of the substituent in the alkanediyl group represented byA^(a41) include a hydroxy group and an alkoxy group having 1 to 6 carbonatoms.

A^(a41) is preferably an alkanediyl group having 1 to 4 carbon atoms,more preferably an alkanediyl group having 2 to 4 carbon atoms, andstill more preferably an ethylene group.

Examples of the divalent saturated hydrocarbon group represented byA^(a42), A^(a43) and A^(a44) in the group represented by formula (a-g1)include a linear or branched alkanediyl group and a monocyclic divalentalicyclic saturated hydrocarbon group, and divalent saturatedhydrocarbon groups formed by combining an alkanediyl group and adivalent alicyclic saturated hydrocarbon group. Specific examplesthereof include a methylene group, an ethylene group, a propane-1,3-diylgroup, a propane-1,2-diyl group, a butane-1,4-diyl group, a1-methylpropane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a2-methylpropane-1,2-diyl group and the like.

Examples of the substituent of the divalent saturated hydrocarbon grouprepresented by A^(a42), A^(a43) and A^(a44) include a hydroxy group andan alkoxy group having 1 to 6 carbon atoms.

s is preferably 0.

In a group represented by formula (a-g1), examples of the group in whichX^(a42) is —O—, —CO—, —CO—O— or —O—CO-include the following groups. Inthe following exemplification, * and ** each represent a bonding site,and ** is a bonding site to —O—CO—R^(a42).

Examples of the structural unit represented by formula (a4-1) includethe following structural units, and structural units in which a methylgroup corresponding to A^(a41) in the structural unit represented byformula (a4-1) in the following structural units is substituted with ahydrogen atom.

Examples of the structural unit represented by formula (a4-1) include astructural unit represented by formula (a4-2) and a structural unitrepresented by formula (a4-3):

wherein, in formula (a4-2),

-   -   R^(f5) represents a hydrogen atom or a methyl group,    -   L⁴⁴ represents an alkanediyl group having 1 to 6 carbon atoms,        and —CH₂— included in the alkanediyl group may be replaced by        —O— or —CO—,    -   R^(f5) represents a saturated hydrocarbon group having 1 to 20        carbon atoms having a fluorine atom, and    -   the upper limit of the total number of carbon atoms of L⁴⁴ and        R^(f6) is 21.

Examples of the alkanediyl group having 1 to 6 carbon atoms of L⁴⁴include the same groups as mentioned for A^(a41).

Examples of the saturated hydrocarbon group of R^(f6) include the samegroups as mentioned for R⁴².

The alkanediyl group in L⁴⁴ is preferably an alkanediyl group having 2to 4 carbon atoms, and more preferably an ethylene group.

The structural unit represented by formula (a4-2) includes, for example,structural units represented by formula (a4-1-1) to formula (a4-1-11). Astructural unit in which a methyl group corresponding to R^(f5) in thestructural unit (a4-2) is substituted with a hydrogen atom is alsoexemplified as the structural unit represented by formula (a4-2):

wherein, in formula (a4-3),

-   -   R^(f7) represents a hydrogen atom or a methyl group,    -   L⁵ represents an alkanediyl group having 1 to 6 carbon atoms,    -   A^(f13) represents a divalent saturated hydrocarbon group having        1 to 18 carbon atoms optionally having a fluorine atom,    -   X^(f12) represents *—O—CO— or *—CO—O— (* represents a bonding        site to A^(f13)),    -   A^(f14) represents a saturated hydrocarbon group having 1 to 17        carbon atoms optionally having a fluorine atom, and    -   at least one of A^(f13) and A^(f14) has a fluorine atom, and the        upper limit of the total number of carbon atoms of L⁵, A^(f13)        and A^(f14) is 20.

Examples of the alkanediyl group in L⁵ include those which are the sameas mentioned in the alkanediyl group of A^(a41).

The divalent saturated hydrocarbon group optionally having a fluorineatom in A^(f13) is preferably a divalent chain saturated hydrocarbongroup optionally having a fluorine atom and a divalent alicyclicsaturated hydrocarbon group optionally having a fluorine atom, and morepreferably a perfluoroalkanediyl group.

Examples of the divalent chain saturated hydrocarbon group optionallyhaving a fluorine atom include alkanediyl groups such as a methylenegroup, an ethylene group, a propanediyl group, a butanediyl group and apentanediyl group; and perfluoroalkanediyl groups such as adifluoromethylene group, a perfluoroethylene group, aperfluoropropanediyl group, a perfluorobutanediyl group and aperfluoropentanediyl group.

The divalent alicyclic saturated hydrocarbon group optionally having afluorine atom may be either monocyclic or polycyclic. Examples of themonocyclic group include a cyclohexanediyl group and aperfluorocyclohexanediyl group. Examples of the polycyclic group includean adamantanediyl group, a norbornanediyl group, aperfluoroadamantanediyl group and the like.

Examples of the saturated hydrocarbon group and the saturatedhydrocarbon group optionally having a fluorine atom for A^(f14) includethe same groups as mentioned for R^(a42). Among these groups, preferredare fluorinated alkyl groups such as a trifluoromethyl group, adifluoromethyl group, a methyl group, a perfluoroethyl group, a2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethylgroup, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, apropyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutylgroup, a butyl group, a perfluoropentyl group, a2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl group,a perfluorohexyl group, a heptyl group, a perfluoroheptyl group, anoctyl group and a perfluorooctyl group; a cyclopropylmethyl group, acyclopropyl group, a cyclobutylmethyl group, a cyclopentyl group, acyclohexyl group, a perfluorocyclohexyl group, an adamantyl group, anadamantylmethyl group, an adamantyldimethyl group, a norbornyl group, anorbornylmethyl group, a perfluoroadamantyl group, aperfluoroadamantylmethyl group and the like.

In formula (a4-3), L⁵ is preferably an ethylene group.

The divalent saturated hydrocarbon group of A^(f13) is preferably agroup including a divalent chain saturated hydrocarbon group having 1 to6 carbon atoms and a divalent alicyclic saturated hydrocarbon grouphaving 3 to 12 carbon atoms, and more preferably a divalent chainsaturated hydrocarbon group having 2 to 3 carbon atoms.

The saturated hydrocarbon group of A^(f14) is preferably a groupincluding a chain saturated hydrocarbon group having 3 to 12 carbonatoms and an alicyclic saturated hydrocarbon group having 3 to 12 carbonatoms, and more preferably a group including a chain saturatedhydrocarbon group having 3 to 10 carbon atoms and an alicyclic saturatedhydrocarbon group having 3 to 10 carbon atoms. Among these groups,A^(f14) is preferably a group including an alicyclic saturatedhydrocarbon group having 3 to 12 carbon atoms, and more preferably acyclopropylmethyl group, a cyclopentyl group, a cyclohexyl group, anorbornyl group and an adamantyl group.

The structural unit represented by formula (a4-3) includes, for example,structural units represented by formula (a4-1′-1) to formula (a4-1′-11).A structural unit in which a methyl group corresponding to R^(f7) in thestructural unit (a4-3) is substitute with a hydrogen atom is alsoexemplified as the structural unit represented by formula (a4-3).

It is also possible to exemplify, as the structural unit (a4), astructural unit represented by formula (a4-4):

wherein, in formula (a4-4),

-   -   R^(f21) represents a hydrogen atom or a methyl group,    -   A^(f21) represents —(CH₂)_(j1)—, —(CH₂)_(j2)—O—(CH₂)_(j3)— or        —(CH₂)_(j4)—CO—O— (CH₂)_(j5)—,    -   j1 to j5 each independently represent an integer of 1 to 6, and    -   R^(f22) represents a saturated hydrocarbon group having 1 to 10        carbon atoms having a fluorine atom.

Examples of the saturated hydrocarbon group for R^(f22) include thosewhich are the same as the saturated hydrocarbon group represented byR^(a42). R^(f22) is preferably an alkyl group having 1 to 10 carbonatoms having a fluorine atom or an alicyclic saturated hydrocarbon grouphaving 1 to 10 carbon atoms having a fluorine atom, more preferably analkyl group having 1 to 10 carbon atoms having a fluorine atom, andstill more preferably, an alkyl group having 1 to 6 carbon atoms havinga fluorine atom.

In formula (a4-4), A^(f21) is preferably —(CH₂)_(j1)—, more preferablyan ethylene group or a methylene group, and still more preferably amethylene group.

The structural unit represented by formula (a4-4) includes, for example,the following structural units and structural units in which a methylgroup corresponding to R^(f21) in the structural unit (a4-4) issubstituted with a hydrogen atom in structural units represented by thefollowing formulas.

When the resin (A) includes the structural unit (a4), the content ispreferably 1 to 20 mol %, more preferably 2 to 15 mol %, and still morepreferably 3 to 10 mol %, based on all structural units of the resin(A).

<Structural Unit (a5)>

Examples of a non-leaving hydrocarbon group possessed by the structuralunit (a5) include groups having a linear, branched or cyclic hydrocarbongroup. Among these, the structural unit (a5) is preferably a grouphaving an alicyclic hydrocarbon group.

The structural unit (a5) includes, for example, a structural unitrepresented by formula (a5-1):

wherein, in formula (a5-1),

-   -   R⁵¹ represents a hydrogen atom or a methyl group,    -   R⁵² represents an alicyclic hydrocarbon group having 3 to 18        carbon atoms, and a hydrogen atom included in the alicyclic        hydrocarbon group may be substituted with an aliphatic        hydrocarbon group having 1 to 8 carbon atoms, and    -   L⁵⁵ represents a single bond or a divalent saturated hydrocarbon        group having 1 to 18 carbon atoms, and —CH₂-included in the        saturated hydrocarbon group may be replaced by —O— or —CO—.

The alicyclic hydrocarbon group in R⁵² may be either monocyclic orpolycyclic. The monocyclic alicyclic hydrocarbon group includes, forexample, a cyclopropyl group, a cyclobutyl group, a cyclopentyl groupand a cyclohexyl group. The polycyclic alicyclic hydrocarbon groupincludes, for example, an adamantyl group and a norbornyl group.

The aliphatic hydrocarbon group having 1 to 8 carbon atoms includes, forexample, alkyl groups such as a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, a sec-butyl group, atert-butyl group, a pentyl group, a hexyl group, an octyl group and a2-ethylhexyl group.

Examples of the alicyclic hydrocarbon group having a substituentincludes a 3-methyladamantyl group and the like.

R⁵² is preferably an unsubstituted alicyclic hydrocarbon group having 3to 18 carbon atoms, and more preferably an adamantyl group, a norbornylgroup or a cyclohexyl group.

Examples of the divalent saturated hydrocarbon group in L⁵⁶ include adivalent chain saturated hydrocarbon group and a divalent alicyclicsaturated hydrocarbon group, and a divalent chain saturated hydrocarbongroup is preferred.

The divalent chain saturated hydrocarbon group includes, for example,alkanediyl groups such as a methylene group, an ethylene group, apropanediyl group, a butanediyl group and a pentanediyl group.

The divalent alicyclic saturated hydrocarbon group may be eithermonocyclic or polycyclic. Examples of the monocyclic alicyclic saturatedhydrocarbon group include cycloalkanediyl groups such as acyclopentanediyl group and a cyclohexanediyl group. Examples of thepolycyclic divalent alicyclic saturated hydrocarbon group include anadamantanediyl group and a norbornanediyl group.

The group in which —CH₂— included in the divalent saturated hydrocarbongroup represented by L⁵⁵ is replaced by —O— or —CO— includes, forexample, groups represented by formula (L1-1) to formula (L1-4). In thefollowing formulas, * and ** each represent a bonding site, and *represents a bonding site to an oxygen atom.

In formula (L1-1),

-   -   X^(x1) represents *—O—CO— or *—CO—O— (* represents a bonding        site to L^(x1)),    -   L^(x1) represents a divalent aliphatic saturated hydrocarbon        group having 1 to 16 carbon atoms,    -   L^(x2) represents a single bond or a divalent aliphatic        saturated hydrocarbon group having 1 to 15 carbon atoms, and    -   the total number of carbon atoms of L^(x1) and L^(x2) is 16 or        less.

In formula (L1-2),

-   -   L^(x3) represents a divalent aliphatic saturated hydrocarbon        group having 1 to 17 carbon atoms,    -   L^(x4) represents a single bond or a divalent aliphatic        saturated hydrocarbon group having 1 to 16 carbon atoms, and    -   the total number of carbon atoms of L^(x3) and L^(x4) is 17 or        less.

In formula (L1-3),

-   -   L^(x5) represents a divalent aliphatic saturated hydrocarbon        group having 1 to 15 carbon atoms,    -   L^(x6) and L^(x7) each independently represent a single bond or        a divalent aliphatic saturated hydrocarbon group having 1 to 14        carbon atoms, and    -   the total number of carbon atoms of L^(x5), L^(x6), and L^(x7)        is 15 or less.

In formula (L1-4),

-   -   L^(x8) and L^(x9) represents a single bond or a divalent        aliphatic saturated hydrocarbon group having 1 to 12 carbon        atoms,    -   W^(x1) represents a divalent alicyclic saturated hydrocarbon        group having 3 to 15 carbon atoms, and    -   the total number of carbon atoms of L^(x8), L^(x9) and W^(x1) is        15 or less.    -   L^(x1) is preferably a divalent aliphatic saturated hydrocarbon        group having 1 to 8 carbon atoms, and more preferably a        methylene group or an ethylene group.    -   L^(x2) is preferably a single bond or a divalent aliphatic        saturated hydrocarbon group having 1 to 8 carbon atoms, and more        preferably a single bond.    -   L^(x3) is preferably a divalent aliphatic saturated hydrocarbon        group having 1 to 8 carbon atoms.    -   L^(x4) is preferably a single bond or a divalent aliphatic        saturated hydrocarbon group having 1 to 8 carbon atoms.    -   L^(x5) is preferably a divalent aliphatic saturated hydrocarbon        group having 1 to 8 carbon atoms, and more preferably a        methylene group or an ethylene group.    -   L^(x6) is preferably a single bond or a divalent aliphatic        saturated hydrocarbon group having 1 to 8 carbon atoms, and more        preferably a methylene group or an ethylene group.    -   L^(x7) is preferably a single bond or a divalent aliphatic        saturated hydrocarbon group having 1 to 8 carbon atoms.    -   L^(x8) is preferably a single bond or a divalent aliphatic        saturated hydrocarbon group having 1 to 8 carbon atoms, and more        preferably a single bond or a methylene group.    -   L^(x9) is preferably a single bond or a divalent aliphatic        saturated hydrocarbon group having 1 to 8 carbon atoms, and more        preferably a single bond or a methylene group.    -   W^(x1) is preferably a divalent alicyclic saturated hydrocarbon        group having 3 to 10 carbon atoms, and more preferably a        cyclohexanediyl group or an adamantanediyl group.

The group represented by formula (L1-1) includes, for example, thefollowing divalent groups.

The group represented by formula (L1-2) includes, for example, thefollowing divalent groups.

The group represented by formula (L1-3) includes, for example, thefollowing divalent groups.

The group represented by formula (L1-4) includes, for example, thefollowing divalent groups.

L⁵⁵ is preferably a single bond or a group represented by formula(L1-1).

Examples of the structural unit (a5-1) include the following structuralunits and structural units in which a methyl group corresponding to R⁵¹in the structural unit (a5-1) in the following structural units issubstituted with a hydrogen atom.

When the resin (A) includes the structural unit (a5), the content ispreferably 1 to 30 mol %, more preferably 2 to 20 mol %, and still morepreferably 3 to 15 mol %, based on all structural units of the resin(A).

<Structural Unit (II)>

The resin (A) may further include a structural unit which is decomposedupon exposure to radiation to generate an acid (hereinafter sometimesreferred to as “structural unit (II)). Specific examples of thestructural unit (II) include the structural units mentioned in JP2016-79235 A, and a structural unit having a sulfonate group or acarboxylate group and an organic cation in a side chain or a structuralunit having a sulfonio group and an organic anion in a side chain arepreferred.

The structural unit having a sulfonate group or a carboxylate group andan organic cation in a side chain is preferably a structural unitrepresented by formula (II-2-A′):

wherein, in formula (II-2-A′),

-   -   X^(III3) represents a divalent saturated hydrocarbon group        having 1 to 18 carbon atoms, —CH₂— included in the saturated        hydrocarbon group may be replaced by —O—, —S— or —CO—, and a        hydrogen atom included in the saturated hydrocarbon group may be        substituted with a halogen atom, an alkyl group having 1 to 6        carbon atoms optionally having a halogen atom, or a hydroxy        group,    -   A^(x1) represents an alkanediyl group having 1 to 8 carbon        atoms, and a hydrogen atom included in the alkanediyl group may        be substituted with a fluorine atom or a perfluoroalkyl group        having 1 to 6 carbon atoms,    -   RA⁻ represents a sulfonate group or a carboxylate group,    -   R^(III3) represents a hydrogen atom, a halogen atom or an alkyl        group having 1 to 6 carbon atoms optionally having a halogen        atom, and    -   ZA⁺ represents an organic cation.

Examples of the halogen atom represented by R^(III3) include a fluorineatom, a chlorine atom, a bromine atom and an iodine atom.

Examples of the alkyl group having 1 to 6 carbon atoms optionally havinga halogen atom represented by R^(III3) include those which are the sameas the alkyl group having 1 to 6 carbon atoms optionally having ahalogen atom represented by R^(a8).

Examples of the alkanediyl group having 1 to 8 carbon atoms representedby A^(x1) include a methylene group, an ethylene group, apropane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diylgroup, a hexane-1,6-diyl group, a ethane-1,1-diyl group, apropane-1,1-diyl group, a propane-1,2-diyl group, a propane-2,2-diylgroup, a pentane-2,4-diyl group, a 2-methylpropane-1,3-diyl group, a2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group, a2-methylbutane-1,4-diyl group and the like.

Examples of the perfluoroalkyl group having 1 to 6 carbon atoms in whicha hydrogen atom may be substituted in A^(x1) include a trifluoromethylgroup, a perfluoroethyl group, a perfluoropropyl group, aperfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butylgroup, a perfluorotert-butyl group, a perfluoropentyl group, aperfluorohexyl group and the like.

Examples of the divalent saturated hydrocarbon group having 1 to 18carbon atoms represented by X^(III3) include a linear or branchedalkanediyl group, a monocyclic or a polycyclic divalent alicyclicsaturated hydrocarbon group, or a combination thereof.

Specific examples thereof include linear alkanediyl groups such as amethylene group, an ethylene group, a propane-1,3-diyl group, apropane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diylgroup, a hexane-1,6-diyl group, a heptane-1,7-diyl group, anoctane-1,8-diyl group, a nonane-1,9-diyl group, a decane-1,10-diylgroup, an undecane-1,1-diyl group and a dodecane-1,12-diyl group;branched alkanediyl groups such as a butane-1,3-diyl group, a2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, apentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group; divalentmonocyclic alicyclic saturated hydrocarbon groups such as acyclobutane-1,3-diyl group, a cyclopentane-1,3-diyl group, acyclohexane-1,4-diyl group and a cyclooctane-1,5-diyl group; anddivalent polycyclic alicyclic saturated hydrocarbon groups such as anorbornane-1,4-diyl group, a norbornane-2,5-diyl group, anadamantane-1,5-diyl group and an adamantane-2,6-diyl group.

Those in which —CH₂— included in the saturated hydrocarbon group arereplaced by —O—, —S— or —CO— include, for example, divalent groupsrepresented by formula (X1) to formula (X53). Before replacing —CH₂—included in the saturated hydrocarbon group by —O—, —S— or —CO—, thenumber of carbon atoms is 17 or less. In the following formulas, * and** represent a bonding site, and * represents a bonding site to A^(x1).

-   -   X³ represents a divalent saturated hydrocarbon group having 1 to        16 carbon atoms.    -   X⁴ represents a divalent saturated hydrocarbon group having 1 to        15 carbon atoms.    -   X⁵ represents a divalent saturated hydrocarbon group having 1 to        13 carbon atoms.    -   X⁶ represents a divalent saturated hydrocarbon group having 1 to        14 carbon atoms.    -   X⁷ represents a trivalent saturated hydrocarbon group having 1        to 14 carbon atoms.    -   X⁸ represents a divalent saturated hydrocarbon group having 1 to        13 carbon atoms.

Examples of the organic cation represented by ZA⁺ include those whichare the same as the cation Z1⁺ in the salt (B1).

The structural unit represented by formula (II-2-A′) is preferably astructural unit represented by formula (I-2-A):

wherein, in formula (II-2-A), R^(III3), X^(III3) and ZA⁺ are the same asdefined above,

-   -   z represents an integer of 0 to 6,    -   R^(III2) and R^(III4) each independently represent a hydrogen        atom, a fluorine atom or a perfluoroalkyl group having 1 to 6        carbon atoms, and when z is 2 or more, a plurality of R^(III2)        and R^(III4) may be the same or different from each other, and    -   Q^(a) and Q^(b) each independently represent a fluorine atom or        a perfluoroalkyl group having 1 to 6 carbon atoms.

Examples of the perfluoroalkyl group having 1 to 6 carbon atomsrepresented by R^(III2), R^(III4), Q^(a) and Q^(b) include those whichare the same as the perfluoroalkyl group having 1 to 6 carbon atomsrepresented by Q^(b1).

The structural unit represented by formula (II-2-A) is preferably astructural unit represented by formula (II-2-A-1):

wherein, in formula (II-2-A-1),

-   -   R^(III2), R^(III3), R^(III4), Q^(a), Q^(b), z and ZA⁺ are the        same as defined above,    -   R^(III5) represents a saturated hydrocarbon group having 1 to 12        carbon atoms, and    -   X^(I2) represents a divalent saturated hydrocarbon group having        1 to 11 carbon atoms, —CH₂— included in the saturated        hydrocarbon group may be replaced by —O—, —S— or —CO—, and a        hydrogen atom included in the saturated hydrocarbon group may be        substituted with a halogen atom or a hydroxy group.

Examples of the saturated hydrocarbon group having 1 to 12 carbon atomsrepresented by R^(III5) include linear or branched alkyl groups such asa methyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, ahexyl group, a heptyl group, an octyl group, a nonyl group, a decylgroup, an undecyl group and a dodecyl group.

Examples of the divalent saturated hydrocarbon group represented byX^(I2) include those which are the same as the divalent saturatedhydrocarbon group represented by X^(III3).

The structural unit represented by formula (II-2-A-1) is preferably astructural unit represented by formula (II-2-A-2):

wherein, in formula (II-2-A-2), R^(III3), R^(III5) and ZA⁺ are the sameas defined above, and

-   -   m and n each independently represent 1 or 2.

The structural unit represented by formula (II-2-A′) includes, forexample, the following structural units and the structural unitsmentioned in WO 2012/050015 A. ZA⁺ represents an organic cation.

The structural unit having a sulfonio group and an organic anion in aside chain is preferably a structural unit represented by formula(II-1-1):

wherein, in formula (II-1-1),

-   -   A^(II1) represents a single bond or a divalent linking group,    -   R^(II1) represents a divalent aromatic hydrocarbon group having        6 to 18 carbon atoms,    -   R^(II2) and R^(II3) each independently represent a hydrocarbon        group having 1 to 18 carbon atoms, and R^(II2) and R^(II3) may        be bonded to each other to form a ring together with sulfur        atoms to which R^(II2) and R^(II3) are bonded,    -   R^(II4) represents a hydrogen atom, a halogen atom or an alkyl        group having 1 to 6 carbon atoms optionally having a halogen        atom, and    -   A⁻ represents an organic anion.

Examples of the divalent aromatic hydrocarbon group having 6 to 18carbon atoms represented by R^(III) include a phenylene group and anaphthylene group.

Examples of the hydrocarbon group represented by R^(II2) and R^(II3)include an alkyl group, an alicyclic hydrocarbon group, an aromatichydrocarbon group, and groups formed by combining these groups.

Examples of the alkyl group and the alicyclic hydrocarbon group includethose which are the same as mentioned above.

Examples of the aromatic hydrocarbon group include aryl groups such as aphenyl group, a naphthyl group, an anthryl group, a biphenyl group and aphenanthryl group.

Examples of the combined group include groups obtained by combining theabove-mentioned alkyl groups and alicyclic hydrocarbon groups, aralkylgroups such as a benzyl group, aromatic hydrocarbon groups having analkyl group (a p-methylphenyl group, a p-tert-butylphenyl group, a tolylgroup, a xylyl group, a cumenyl group, a mesityl group, a2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.), aromatichydrocarbon groups having an alicyclic hydrocarbon group (ap-cyclohexylphenyl group, a p-adamantylphenyl group, etc.),aryl-cycloalkyl groups such as a phenylcyclohexyl group and the like.

Examples of the halogen atom represented by R^(II4) include a fluorineatom, a chlorine atom, a bromine atom and an iodine atom.

Examples of the alkyl group having 1 to 6 carbon atoms optionally havinga halogen atom represented by R^(II4) include those which are the sameas the alkyl group having 1 to 6 carbon atoms optionally having ahalogen atom represented by R^(a8).

Examples of the divalent linking group represented by A^(II1) include adivalent saturated hydrocarbon group having 1 to 18 carbon atoms, and—CH₂— included in the divalent saturated hydrocarbon group may bereplaced by —O—, —S— or —CO—. Specific examples thereof include thosewhich are the same as the divalent saturated hydrocarbon group having 1to 18 carbon atoms represented by X^(II3):

Examples of the structural unit including a cation in formula (II-1-1)include the following structural units.

Examples of the organic anion represented by A⁻ include a sulfonic acidanion, a sulfonylimide anion, a sulfonylmethide anion and a carboxylicacid anion. The organic anion represented by A⁻ is preferably a sulfonicacid anion, and examples of the sulfonic acid anion, the sulfonylimideanion, the sulfonylmethide anion and the carboxylic acid anion includethose which are the same as the anion include in the salt represented byformula (I).

Examples of the structural unit represented by formula (II-1-1) includestructural units represented by the followings.

When the structural unit (II) is included in the resin (A), the contentof the structural unit (IT) is preferably 1 to 20 mol %, more preferably2 to 15 mol %, and still more preferably 3 to 10 mol %, based on allstructural units of the resin (A).

The resin (A) may include structural units other than the structuralunits mentioned above, and examples of such structural unit includestructural units well-known in the art.

The resin (A) is preferably a resin composed of a structural unit (a1)and a structural unit (s), i.e. a copolymer of a monomer (a1) and amonomer (s).

The structural unit (a1) is preferably at least one selected from thegroup consisting of a structural unit (a1-0), a structural unit (a1-1)and a structural unit (a1-2) (preferably the structural unit having acyclohexyl group, and a cyclopentyl group), more preferably at leasttwo, and still more preferably at least two selected from the groupconsisting of a structural unit (a1-1) and a structural unit (a1-2).

The structural unit (s) is preferably at least one selected from thegroup consisting of a structural unit (a2) and a structural unit (a3).The structural unit (a2) is preferably a structural unit represented byformula (a2-1) or a structural unit represented by formula (a2-A). Thestructural unit (a3) is preferably at least one selected from the groupconsisting of a structural unit represented by formula (a3-1), astructural unit represented by formula (a3-2) and a structural unitrepresented by formula (a3-4).

The respective structural units constituting the resin (A) may be usedalone, or two or more structural units may be used in combination. Usinga monomer from which these structural units are derived, it is possibleto produce by a known polymerization method (e.g. radical polymerizationmethod). The content of the respective structural units included in theresin (A) can be adjusted according to the amount of the monomer used inthe polymerization.

The weight-average molecular weight of the resin (A) is preferably 2,000or more (more preferably 2,500 or more, and still more preferably 3,000or more), and 50,000 or less (more preferably 30,000 or less, and stillmore preferably 15,000 or less). In the present specification, theweight-average molecular weight is a value determined by gel permeationchromatography under the conditions mentioned in Examples.

<Resin Other than Resin (A)>

The resist composition of the present invention may include a resinother than the resin (A), in addition to the resin (A).

The resin other than the resin (A) includes, for example, a resinincluding a structural unit (a4) or a structural unit (a5) (hereinaftersometimes referred to as resin (X)).

The resin (X) is preferably a resin including a structural unit (a4),particularly.

In the resin (X), the content of the structural unit (a4) is preferably30 mol % or more, more preferably 40 mol % or more, and still morepreferably 45 mol % or more, based on the total of all structural unitsof the resin (X).

Examples of the structural unit, which may be further included in theresin (X), include a structural unit (a2), a structural unit (a3) andstructural units derived from other known monomers. Particularly, theresin (X) is preferably a resin composed only of a structural unit (a4)and/or a structural unit (a5), and more preferably a resin composed onlyof a structural unit (a4).

The respective structural unit constituting the resin (X) may be usedalone, or two or more structural units may be used in combination. Usinga monomer from which these structural units are derived, it is possibleto produce by a known polymerization method (e.g. radical polymerizationmethod). The content of the respective structural units included in theresin (X) can be adjusted according to the amount of the monomer used inthe polymerization.

The weight-average molecular weight of the resin (X) is preferably 6,000or more (more preferably 7,000 or more), and 80,000 or less (morepreferably 60,000 or less). The measurement means of the weight-averagemolecular weight of the resin (X) is the same as in the case of theresin (A).

When the resist composition includes the resin (X), the content ispreferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass,still more preferably 1 to 40 parts by mass, particularly preferably 1to 30 parts by mass, and particularly preferably 1 to 8 parts by mass,based on 100 parts by mass of the resin (A).

The content of the resin (A) in the resist composition is preferably 80%by mass or more and 99% by mass or less, and more preferably 90% by massor more and 99% by mass or less, based on the solid component of theresist composition. When including resins other than the resin (A), thetotal content of the resin (A) and resins other than the resin (A) ispreferably 80% by mass or more and 99% by mass or less, and morepreferably 90% by mass or more and 99% by mass or less, based on thesolid component of the resist composition. In the present specification,“solid component of the resist composition” means the total amount ofcomponents obtained by removing a solvent (E) mentioned later from thetotal amount of the resist composition. The solid component of theresist composition and the content of the resin thereto can be measuredby a known analysis means such as liquid chromatography or gaschromatography.

<Solvent (E)>

The content of the solvent (E) in the resist composition is usually 90%by mass or more and 99.9% by mass or less, preferably 92% by mass ormore and 99% by mass or less, and more preferably 94% by mass or moreand 99% by mass or less. The content of the solvent (E) can be measured,for example, by a known analysis means such as liquid chromatography orgas chromatography.

Examples of the solvent (E) include glycol ether esters such asethylcellosolve acetate, methylcellosolve acetate and propylene glycolmonomethyl ether acetate; glycol ethers such as propylene glycolmonomethyl ether; esters such as ethyl lactate, butyl acetate, amylacetate and ethyl pyruvate; ketones such as acetone, methyl isobutylketone, 2-heptanone and cyclohexanone; and cyclic esters such asγ-butyrolactone. The solvent (E) may be used alone, or two or moresolvents may be used.

<Quencher (C)>

Examples of the quencher (C) include a basic nitrogen-containing organiccompound, and a salt generating an acid having an acidity lower thanthat of an acid generated from an acid generator (B). The content of thequencher (C) is preferably about 0.01 to 5% by mass based on the amountof the solid component of the resist composition.

Examples of the basic nitrogen-containing organic compound include amineand an ammonium salt. Examples of the amine include an aliphatic amineand an aromatic amine. Examples of the aliphatic amine include a primaryamine, a secondary amine and a tertiary amine.

Examples of the amine include 1-naphthylamine, 2-naphthylamine, aniline,diisopropylaniline, 2-, 3- or 4-methylaniline, 4-nitroaniline,N-methylaniline, N,N-dimethylaniline, diphenylamine, hexylamine,heptylamine, octylamine, nonylamine, decylamine, dibutylamine,dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine,didecylamine, triethylamine, trimethylamine, tripropylamine,tributylamine, tripentylamine, trihexylamine, triheptylamine,trioctylamine, trinonylamine, tridecylamine, methyldibutylamine,methyldipentylamine, methyldihexylamine, methyldicyclohexylamine,methyldiheptylamine, methyldioctylamine, methyldinonylamine,methyldidecylamine, ethyldibutylamine, ethyldipentylamine,ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine,ethyldinonylamine, ethyldidecylamine, dicyclohexylmethylamine,tris[2-(2-methoxyethoxy)ethyl]amine, triisopropanolamine,ethylenediamine, tetramethylenediamine, hexamethylenediamine,4,4′-diamino-1,2-diphenylethane,4,4′-diamino-3,3′-dimethyldiphenylmethane,4,4′-diamino-3,3′-diethyldiphenylmethane, 2,2′-methylenebisaniline,imidazole, 4-methylimidazole, pyridine, 4-methylpyridine,1,2-di(2-pyridyl)ethane, 1,2-di(4-pyridyl)ethane,1,2-di(2-pyridyl)ethene, 1,2-di(4-pyridyl)ethene,1,3-di(4-pyridyl)propane, 1,2-di(4-pyridyloxy)ethane, di(2-pyridyl)ketone, 4,4′-dipyridyl sulfide, 4,4′-dipyridyl disulfide,2,2′-dipyridylamine, 2,2′-dipicolylamine, bipyridine and the like,preferably aromatic amines such as diisopropylaniline, and morepreferably 2,6-diisopropylaniline.

Examples of the ammonium salt include tetramethylammonium hydroxide,tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide,tetrahexylammonium hydroxide, tetraoctylammonium hydroxide,phenyltrimethylammonium hydroxide,3-(trifluoromethyl)phenyltrimethylammonium hydroxide,tetra-n-butylammonium salicylate and choline.

The acidity in a salt generating an acid having an acidity lower thanthat of an acid generated from the acid generator (B) is indicated bythe acid dissociation constant (pKa). Regarding the salt generating anacid having an acidity lower than that of an acid generated from theacid generator (B), the acid dissociation constant of an acid generatedfrom the salt usually meets the following inequality: −3<pKa, preferably−1<pKa<7, and more preferably 0<pKa<5.

Examples of the salt generating an acid having an acidity lower thanthat of an acid generated from the acid generator (B) include saltsrepresented by the following formulas, a salt represented by formula (D)mentioned in JP 2015-147926 A (hereinafter sometimes referred to as“weak acid inner salt (D)”, and salts mentioned in JP 2012-229206 A, JP2012-6908 A, JP 2012-72109 A, JP 2011-39502 A and JP 2011-191745 A. Thesalt generating an acid having an acidity lower than that of an acidgenerated from the acid generator (B) is preferably a weak acid innersalt (D).

Examples of the weak acid inner salt (D) include the following salts.

When the resist composition includes the quencher (C), the content ofthe quencher (C) in the solid component of the resist composition isusually 0.01 to 5% by mass, and preferably 0.01 to 3% by mass.

<Other Components>

The resist composition of the present invention may also includecomponents other than the components mentioned above (hereinaftersometimes referred to as “other components (F)”). The other components(F) are not particularly limited and it is possible to use variousadditives known in the resist field, for example, sensitizers,dissolution inhibitors, surfactants, stabilizers and dyes.

<Preparation of Resist Composition>

The resist composition of the present invention can be prepared bymixing a salt (I) and a resin (A), and if necessary, an acid generator(B), resins other than the resin (A), a solvent (E), a quencher (C) andother components (F). The order of mixing these components is any orderand is not particularly limited. It is possible to select, as thetemperature during mixing, appropriate temperature from 10 to 40° C.,according to the type of the resin, the solubility in the solvent (E) ofthe resin and the like. It is possible to select, as the mixing time,appropriate time from 0.5 to 24 hours according to the mixingtemperature. The mixing means is not particularly limited and it ispossible to use mixing with stirring.

After mixing the respective components, the mixture is preferablyfiltered through a filter having a pore diameter of about 0.003 to 0.2μm.

<Method for Producing Resist Pattern>

The method for producing a resist pattern of the present inventioninclude:

-   -   (1) a step of applying the resist composition of the present        invention on a substrate,    -   (2) a step of drying the applied composition to form a        composition layer,    -   (3) a step of exposing the composition layer,    -   (4) a step of heating the exposed composition layer, and    -   (5) a step of developing the heated composition layer.

The resist composition can be usually applied on a substrate using aconventionally used apparatus, such as a spin coater. Examples of thesubstrate include inorganic substrates such as a silicon wafer. Beforeapplying the resist composition, the substrate may be washed, and anorganic antireflection film may be formed on the substrate.

The solvent is removed by drying the applied composition to form acomposition layer. Drying is performed by evaporating the solvent usinga heating device such as a hot plate (so-called “prebake”), or adecompression device. The heating temperature is preferably 50 to 200°C. and the heating time is preferably 10 to 180 seconds. The pressureduring drying under reduced pressure is preferably about 1 to 1.0×10⁵Pa.

The composition layer thus obtained is usually exposed using an aligner.The aligner may be a liquid immersion aligner. It is possible to use, asan exposure source, various exposure sources, for example, exposuresources capable of emitting laser beam in an ultraviolet region such asKrF excimer laser (wavelength of 248 nm), ArF excimer laser (wavelengthof 193 nm) and F₂ excimer laser (wavelength of 157 nm), an exposuresource capable of emitting harmonic laser beam in a far-ultraviolet orvacuum ultra violet region by wavelength-converting laser beam from asolid-state laser source (YAG or semiconductor laser), an exposuresource capable of emitting electron beam or EUV and the like. In thepresent specification, such exposure to radiation is sometimescollectively referred to as “exposure”. The exposure is usuallyperformed through a mask corresponding to a pattern to be required. Whenelectron beam is used as the exposure source, exposure may be performedby direct writing without using the mask.

The exposed composition layer is subjected to a heat treatment(so-called “post-exposure bake”) to promote the deprotection reaction inan acid-labile group. The heating temperature is usually about 50 to200° C., and preferably about 70 to 150° C.

The heated composition layer is usually developed with a developingsolution using a development apparatus. Examples of the developingmethod include a dipping method, a paddle method, a spraying method, adynamic dispensing method and the like. The developing temperature ispreferably, for example, 5 to 60° C. and the developing time ispreferably, for example, 5 to 300 seconds. It is possible to produce apositive resist pattern or negative resist pattern by selecting the typeof the developing solution as follows.

When the positive resist pattern is produced from the resist compositionof the present invention, an alkaline developing solution is used as thedeveloping solution. The alkaline developing solution may be variousaqueous alkaline solutions used in this field. Examples thereof includeaqueous solutions of tetramethylammonium hydroxide and(2-hydroxyethyl)trimethylammonium hydroxide (commonly known as choline).The surfactant may be contained in the alkaline developing solution.

It is preferred that the developed resist pattern is washed withultrapure water and then water remaining on the substrate and thepattern is removed.

When the negative resist pattern is produced from the resist compositionof the present invention, a developing solution containing an organicsolvent (hereinafter sometimes referred to as “organic developingsolution”) is used as the developing solution.

Examples of the organic solvent contained in the organic developingsolution include ketone solvents such as 2-hexanone and 2-heptanone;glycol ether ester solvents such as propylene glycol monomethyl etheracetate; ester solvents such as butyl acetate; glycol ether solventssuch as propylene glycol monomethyl ether; amide solvents such asN,N-dimethylacetamide; and aromatic hydrocarbon solvents such asanisole.

The content of the organic solvent in the organic developing solution ispreferably 90% by mass or more and 100% by mass or less, more preferably95% by mass or more and 100% by mass or less, and still more preferablythe organic developing solution is substantially composed of the organicsolvent.

Particularly, the organic developing solution is preferably a developingsolution containing butyl acetate and/or 2-heptanone. The total contentof butyl acetate and 2-heptanone in the organic developing solution ispreferably 50% by mass or more and 100% by mass or less, more preferably90% by mass or more and 100% by mass or less, and still more preferablythe organic developing solution is substantially composed of butylacetate and/or 2-heptanone.

The surfactant may be contained in the organic developing solution. Atrace amount of water may be contained in the organic developingsolution.

During development, the development may be stopped by replacing by asolvent with the type different from that of the organic developingsolution.

The developed resist pattern is preferably washed with a rinsingsolution. The rinsing solution is not particularly limited as long as itdoes not dissolve the resist pattern, and it is possible to use asolution containing an ordinary organic solvent which is preferably analcohol solvent or an ester solvent.

After washing, the rinsing solution remaining on the substrate and thepattern is preferably removed.

<Application>

The resist composition of the present invention is suitable as a resistcomposition for exposure of KrF excimer laser, a resist composition forexposure of ArF excimer laser, a resist composition for exposure ofelectron beam (EB) or a resist composition for exposure of EUV,particularly a resist composition for exposure of electron beam (EB) ora resist composition for exposure of EUV, and the resist composition isuseful for fine processing of semiconductors.

EXAMPLES

The present invention will be described more specifically by way ofExamples. Percentages and parts expressing the contents or amounts usedin the Examples are by mass unless otherwise specified.

The weight-average molecular weight is a value determined by gelpermeation chromatography. Analysis conditions of gel permeationchromatography are as follows.

-   -   Column: TSKgel Multipore IIXL-M×3+guardcolumn (manufactured by        TOSOH CORPORATION)    -   Eluent: tetrahydrofuran    -   Flow rate: 1.0 mL/min    -   Detector: RI detector    -   Column temperature: 40° C.    -   Injection amount: 100 μl    -   Molecular weight standards: polystyrene standard (manufactured        by TOSOH CORPORATION)

Structures of compounds were confirmed by measuring a molecular ion peakusing mass spectrometry (Liquid Chromatography: Model 1100, manufacturedby Agilent Technologies, Inc., Mass Spectrometry: Model LC/MSD,manufactured by Agilent Technologies, Inc.). The value of this molecularion peak in the following Examples is indicated by “MASS”.

Example 1: Synthesis of Salt Represented by Formula (I-2)

5 Parts of a compound represented by formula (I-2-a), 10 parts oftetrahydrofuran and 11.00 parts of trimethylsilyltrifluoromethanesulfonate were mixed, followed by stirring at 23° C. for30 minutes and further cooling to 10° C. A Grignard solution prepared bymixing 1.20 parts of magnesium, 8.65 parts of a compound represented byformula (I-2-b) and 17.30 parts of tetrahydrofuran was added dropwise tothe mixed solution obtained previously at 10° C., followed by stirringat 23° C. for 18 hours. To the mixture thus obtained, 30 parts of 1Nhydrochloric acid and 50 parts of chloroform were added. After stirringat 23° C. for 30 minutes, an organic layer was isolated throughseparation. To the organic layer thus obtained, 30 parts ofion-exchanged water was added and, after stirring at 23° C. for 30minutes, an organic layer was isolated through separation. This waterwashing operation was repeated three times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 3.24 parts of a salt represented by formula (I-2-c).

2.91 Parts of the salt represented by formula (I-2-c), 2.56 parts of asalt represented by formula (I-2-d), 15 parts of chloroform and 30 partsof ion-exchanged water were mixed. After stirring at 23° C. for 2 hours,an organic layer was isolated through separation. To the organic layerthus obtained, 15 parts of 1N hydrochloric acid was added and, afterstirring at 23° C. for 30 minutes, an organic layer was isolated throughseparation. To the organic layer thus obtained, 15 parts ofion-exchanged water was added and, after stirring at 23° C. for 30minutes, an organic layer was isolated through separation. This waterwashing operation was repeated five times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 1.62 parts of a salt represented by formula (I-2).

-   -   MASS (ESI (+) Spectrum): M⁺ 353.0    -   MASS (ESI (−) Spectrum): M⁻ 339.1

Example 2: Synthesis of Salt Represented by Formula (I-3)

2.91 Parts of the salt represented by formula (I-2-c), 2.46 parts of asalt represented by formula (I-3-d)/15 parts of chloroform and 30 partsof ion-exchanged water were mixed. After stirring at 23° C. for 2 hours,an organic layer was isolated through separation. To the organic layerthus obtained, 15 parts of 1N hydrochloric acid was added and, afterstirring at 23° C. for 30 minutes, an organic layer was isolated throughseparation. To the organic layer thus obtained, 15 parts ofion-exchanged water was added and, after stirring at 23° C. for 30minutes, an organic layer was isolated through separation. This waterwashing operation was repeated five times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 1.72 parts of a salt represented by formula (I-3).

-   -   MASS (ESI (+) Spectrum): M⁺ 353.0    -   MASS (ESI (−) Spectrum): M⁻ 323.0

Example 3: Synthesis of Salt Represented by Formula (I-14)

2.91 Parts of the salt represented by formula (I-2-c), 2.46 parts of asalt represented by formula (I-14-d), 15 parts of chloroform and 30parts of ion-exchanged water were mixed. After stirring at 23° C. for 2hours, an organic layer was isolated through separation. To the organiclayer thus obtained, 15 parts of 1N hydrochloric acid was added. Afterstirring at 23° C. for 30 minutes, an organic layer was isolated throughseparation. To the organic layer thus obtained, 15 parts ofion-exchanged water was added and, after stirring at 23° C. for 30minutes, an organic layer was isolated through separation. This waterwashing operation was repeated five times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 2.32 parts of a salt represented by formula (I-14).

-   -   MASS (ESI (+) Spectrum): M⁺ 353.0    -   MASS (ESI (−) Spectrum): M⁻ 323.1

Example 4: Synthesis of Salt Represented by Formula (I-43)

5 Parts of the compound represented by formula (I-2-a), 10 parts oftetrahydrofuran and 11.00 parts of trimethylsilyltrifluoromethanesulfonate were mixed, followed by stirring at 23° C. for30 minutes and further cooling to 10° C. A Grignard solution prepared bymixing 1.20 parts of magnesium, 10.43 parts of a compound represented byformula (I-43-b) and 20.86 parts of tetrahydrofuran was added dropwiseto the mixed solution obtained previously at 10° C., followed bystirring at 23° C. for 18 hours. To the reaction mixture thus obtained,30 parts of 1N hydrochloric acid and 50 parts of chloroform were added.After stirring at 23° C. for 30 minutes, an organic layer was isolatedthrough separation. To the organic layer thus obtained, 30 parts ofion-exchanged water was added and, after stirring at 23° C. for 30minutes, an organic layer was isolated through separation. This waterwashing operation was repeated three times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 3.11 parts of a salt represented by formula (I-43-c).

3.12 Parts of the salt represented by formula (I-43-c), 2.46 parts of asalt represented by formula (I-14-d), 15 parts of chloroform and 30parts of ion-exchanged water were mixed and, after stirring at 23° C.for 2 hours, an organic layer was isolated through separation. To theorganic layer thus obtained, 15 parts of 1N hydrochloric acid was addedand, after stirring at 23° C. for 30 minutes, an organic layer wasisolated through separation. This water washing operation was repeatedfive times. The organic layer thus obtained was concentrated and 30parts of tert-butyl methyl ether was added to the concentrated residue,followed by stirring at 23° C. for 30 minutes. The supernatant wasremoved, followed by concentration to obtain 1.91 parts of a saltrepresented by formula (I-43).

-   -   MASS (ESI (+) Spectrum): M⁺ 389.0    -   MASS (ESI (−) Spectrum): M⁻ 323.1

Example 5: Synthesis of Salt Represented by Formula (I-72)

5 Parts of the compound represented by formula (I-2-a), 10 parts oftetrahydrofuran and 11.00 parts of trimethylsilyltrifluoromethanesulfonate were mixed, followed by stirring at 23° C. for30 minutes and further cooling to 10° C. A Grignard solution prepared bymixing 1.20 parts of magnesium, 9.54 parts of a compound represented byformula (I-72-b) and 19.08 parts of tetrahydrofuran was added dropwiseto the mixed solution obtained previously at 10° C., followed bystirring at 23° C. for 18 hours. To the reaction mixture thus obtained,30 parts of 1N hydrochloric acid and 50 parts of chloroform were addedand, after stirring at 23° C. for 30 minutes, an organic layer wasisolated through separation. To the organic layer thus obtained, 30parts of ion-exchanged water was added and, after stirring at 23° C. for30 minutes, an organic layer was isolated through separation. This waterwashing operation was repeated three times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 1.09 parts of a salt represented by formula (I-72-c).

1.01 Parts of the salt represented by formula (I-72-c), 0.82 part of asalt represented by formula (I-14-d), 10 parts of chloroform and 20parts of ion-exchanged water were mixed and, after stirring at 23° C.for 2 hours, an organic layer was isolated through separation. To theorganic layer thus obtained, 10 parts of 1N hydrochloric acid was addedand, after stirring at 23° C. for 30 minutes, an organic layer wasisolated through separation. To the organic layer thus obtained, 10parts of ion-exchanged water was added and, after stirring at 23° C. for30 minutes, an organic layer was isolated through separation. This waterwashing operation was repeated five times. The organic layer thusobtained was concentrated and 20 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 0.42 part of a salt represented by formula (I-72).

-   -   MASS (ESI (+) Spectrum): M⁺ 371.0    -   MASS (ESI (−) Spectrum): M⁻ 323.1

Example 6: Synthesis of Salt Represented by Formula (I-13)

2.91 Parts of the salt represented by formula (I-2-c), 3.29 parts of asalt represented by formula (I-13-d), 15 parts of chloroform and 30parts of ion-exchanged water were mixed, after stirring at 23° C. for 2hours, an organic layer was isolated through separation. To the organiclayer thus obtained, 15 parts of 1N hydrochloric acid was added and,after stirring at 23° C. for 30 minutes, an organic layer was isolatedthrough separation. To the organic layer thus obtained, 15 parts ofion-exchanged water was added and, after stirring at 23° C. for 30minutes, an organic layer was isolated through separation. This waterwashing operation was repeated five times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 2.11 parts of a salt represented by formula (I-13).

-   -   MASS (ESI (+) Spectrum): M⁺ 353.0    -   MASS (ESI (−) Spectrum): M⁻ 467.1

Example 7: Synthesis of Salt Represented by Formula (I-15)

2.91 Parts of the salt represented by formula (I-2-c), 2.56 parts of asalt represented by formula (I-15-d), 15 parts of chloroform and 30parts of ion-exchanged water were mixed, and after stirring at 23° C.for 2 hours, an organic layer was isolated through separation. To theorganic layer thus obtained, 15 parts of 1N hydrochloric acid was addedand, after stirring at 23° C. for 30 minutes, an organic layer wasisolated through separation. To the organic layer thus obtained, 15parts of ion-exchanged water was added and, after stirring at 23° C. for30 minutes, an organic layer was isolated through separation. This waterwashing operation was repeated five times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 1.89 parts of a salt represented by formula (I-15).

-   -   MASS (ESI (+) Spectrum): M⁺ 353.0    -   MASS (ESI (−) Spectrum): M⁻ 339.1

Example 8: Synthesis of Salt Represented by Formula (I-16)

2.91 Parts of a salt represented by formula (I-2-c), 2.55 parts of asalt represented by formula (I-16-d), 15 parts of chloroform and 30parts of ion-exchanged water were mixed and, after stirring at 23° C.for 2 hours, an organic layer was isolated through separation. To theorganic layer thus obtained, 15 parts of 1N hydrochloric acid was addedand, after stirring at 23° C. for 30 minutes, an organic layer wasisolated through separation. To the organic layer thus obtained, 15parts of ion-exchanged water was added and, after stirring at 23° C. for30 minutes, an organic layer was isolated through separation. This waterwashing operation was repeated five times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 1.81 parts of a salt represented by formula (I-16).

-   -   MASS (ESI (+) Spectrum): M⁺ 353.0    -   MASS (ESI (−) Spectrum): M⁻ 337.1

Example 9: Synthesis of Salt Represented by Formula (I-17)

2.91 Parts of a salt represented by formula (I-2-c), 3.39 parts of asalt represented by formula (I-17-d), 15 parts of chloroform and 30parts of ion-exchanged water were mixed and, after stirring at 23° C.for 2 hours, an organic layer was isolated through separation. To theorganic layer thus obtained, 15 parts of 1N hydrochloric acid was addedand, after stirring at 23° C. for 30 minutes, an organic layer wasisolated through separation. To the organic layer thus obtained, 15parts of ion-exchanged water was added and, after stirring at 23° C. for30 minutes, an organic layer was isolated through separation. This waterwashing operation was repeated five times. The organic layer thusobtained was concentrated and 30 parts of tert-butyl methyl ether wasadded to the concentrated residue, followed by stirring at 23° C. for 30minutes. The supernatant was removed, followed by concentration toobtain 2.88 parts of a salt represented by formula (I-17).

-   -   MASS (ESI (+) Spectrum): M⁺ 353.0    -   MASS (ESI (−) Spectrum): M⁻ 481.1        Synthesis of Resin

Compounds (monomers) used in the synthesis of the resin (A) are shownbelow. Hereinafter, these compounds are referred to as “monomer(a1-1-3)” according to the number of formula.

Synthesis Example 1 ([Synthesis of Resin a1]

Using a monomer(a1-4-2), a monomer (a1-1-3) and a monomer (a1-2-6) asmonomers, these monomers were mixed in a molar ratio of 38:24:38[monomer (a1-4-2):monomer (a1-1-3):monomer (a1-2-6)], and methylisobutyl ketone was added to this monomer mixture in the amount of 1.5mass times the total mass of all monomers. To the mixture thus obtained,azobisisobutyronitrile as an initiator was added in the amount of 7 mol% based on the total molar number of all monomers, and then the mixturewas polymerized by heating at 83° C. for about 5 hours. To thepolymerization reaction mixture thus obtained, an aqueousp-toluenesulfonic acid solution was added. After stirring for 6 hours,an organic layer was isolated through separation. The organic layer thuscollected was poured into a large amount of n-heptane to precipitate aresin, followed by filtration and collection to obtain a resin A1(copolymer) having a weight-average molecular weight of about 5.3×10³ ina yield of 78%. This resin A1 has the following structural units.

Synthesis Example 2 [Synthesis of Resin A2]

Using a monomer (a1-4-2), a monomer (a1-1-3) and a monomer (a1-2-6) asmonomers, these monomers were mixed in a molar ratio of 49:21:30[monomer (a1-4-2):monomer (a1-1-3):monomer (a1-2-6)], and methylisobutyl ketone was added to this monomer mixture in the amount of 1.5mass times the total mass of all monomers. To the mixture thus obtained,azobisisobutyronitrile as an initiator was added in the amount of 7 mol% based on the total molar number of all monomers, and then the mixturewas polymerized by heating at 85° C. for about 5 hours. To thepolymerization reaction mixture thus obtained, an aqueousp-toluenesulfonic acid solution was added. After stirring for 6 hours,an organic layer was isolated through separation. The organic layer thuscollected was poured into a large amount of n-heptane to precipitate aresin, followed by filtration and collection to obtain a resin A2(copolymer) having a weight-average molecular weight of about 5.8×10³ ina yield of 84%. This resin A2 has the following structural units.

Synthesis Example 3 [Synthesis of Resin AX1]

Using a monomer (a1-4-2) and a monomer (a1-2-6) as monomers, thesemonomers were mixed in a molar ratio of 49:51 [monomer (a1-4-2):monomer(a1-2-6)], and methyl isobutyl ketone was added to this monomer mixturein the amount of 1.5 mass times the total mass of all monomers. To themixture thus obtained, azobisisobutyronitrile as an initiator was addedin the amount of 7 mol % based on the total molar number of allmonomers, and then the mixture was polymerized by heating at 85° C. forabout 5 hours. To the polymerization reaction mixture thus obtained, anaqueous p-toluenesulfonic acid solution was added. After stirring for 6hours, an organic layer was isolated through separation. The organiclayer thus collected was poured into a large amount of n-heptane toprecipitate a resin, followed by filtration and collection to obtain aresin AX1 (copolymer) having a weight-average molecular weight of about5.9×10³ in a yield of 88%. This resin AX1 has the following structuralunits.

<Preparation of Resist Compositions>

As shown in Table 2, the following respective components were mixed, andthe mixtures thus obtained were filtered through a fluorine resin filterhaving a pore diameter of 0.2 μm to prepare resist compositions.

TABLE 2 Resist Acid Composition Resin Generator Salt (I) Quencher (C)PB/PEB Composition 1 A1 = 10 parts — I-2 = 1.5 parts C1 = 0.35 part 100°C./130° C. Composition 2 A1 = 10 parts — I-3 = 1.5 parts C1 = 0.35 part100° C./130° C. Composition 3 A1 = 10 parts — I-14 = 1.5 parts C1 = 0.35part 100° C./130° C. Composition 4 A2 = 10 parts — I-14 = 1.5 parts C1 =0.35 part 100° C./130° C. Composition 5 A1 = 10 parts — I-2/I-3 =1.0/0.5 part C1 = 0.35 part 100° C./130° C. Composition 6 A1 = 10 parts— I-43 = 1.5 parts C1 = 0.35 part 100° C./130° C. Composition 7 A1 = 10parts — I-72 = 1.5 parts C1 = 0.35 part 100° C./130° C. Composition 8 A1= 10 parts — I-15 = 1.5 parts C1 = 0.35 part 100° C./130° C. Composition9 A1 = 10 parts — I-16 = 1.5 parts C1 = 0.35 part 100° C./130° C.Composition 10 A1 = 10 parts — I-15/I-16 = 1.0/0.5 part C1 = 0.35 part100° C./130° C. Composition 11 A1 = 10 parts — I-13 = 1.5 parts C1 =0.35 part 100° C./130° C. Composition 12 A1 = 10 parts — I-17 = 1.5parts C1 = 0.35 part 100° C./130° C. Comparative AX1 = 10 parts IX-1 =1.5 parts — C1 = 0.35 part 100° C./130° C. composition 1 Reference A2 =10 parts IX-1 = 1.5 parts — C1 = 0.35 part 100° C./130° C. Composition 1<Resin>

-   -   A1, A2, AX1: resin A1, resin A2, resin X1, resin AX1        <Salt (I)>    -   I-2: Salt represented by formula (I-2)    -   I-3: Salt represented by formula (I-3)    -   I-13: Salt represented by formula (I-13)    -   I-14: Salt represented by formula (I-14)    -   I-15: Salt represented by formula (I-15)    -   I-16: Salt represented by formula (I-16)    -   I-17: Salt represented by formula (I-17)    -   I-43: Salt represented by formula (I-43)    -   I-72: Salt represented by formula (I-72)        <Acid Generator>    -   IX-1: Salt represented by formula (IX-1) (synthesized in        accordance with Examples of JP 2017-015777 A)

<Quencher (C)>

-   -   C1: synthesized by the method mentioned in JP 2011-39502 A

<Solvent (E)>

Propylene glycol monomethyl ether acetate 400 parts Propylene glycolmonomethyl ether 100 parts γ-Butyrolactone 5 parts(Evaluation of Exposure of Resist Composition with Electron Beam)

Each 6 inch-diameter silicon wafer was treated with hexamethyldisilazaneand then baked on a direct hot plate at 90° C. for 60 seconds. A resistcomposition was spin-coated on the silicon wafer so that the thicknessof the composition later became 0.04 μm. The coated silicon wafer wasprebaked on the direct hot plate at the temperature shown in the column“PB” of Table 2 for 60 seconds. Using an electron-beam direct-writesystem (HL-800D 50 keV, manufactured by Hitachi, Ltd.), line-and-spacepatterns were directly written on the composition layer formed on thewafer while changing the exposure dose stepwise.

After the exposure, post-exposure baking was performed on the hot plateat the temperature shown in the column “PEB” of Table 2 for 60 seconds,followed by paddle development with an aqueous 2.38% by masstetramethylammonium hydroxide solution for 60 seconds to obtain a resistpattern.

The resist pattern (line-and-space pattern) thus obtained was observedby a scanning electron microscope and effective sensitivity was definedas the exposure dose at which the resist pattern with 60 nm-1:1 line andspace patterns was obtained.

Evaluation of Line Edge Roughness (LER): Line edge roughness wasdetermined by measuring a roughness width of the irregularity in wallsurface of resist pattern produced by the effective sensitivity using ascanning electron microscope. The results are shown in Table 3.

TABLE 3 Resist Composition LER Example 10 Composition 1 3.82 Example 11Composition 2 3.84 Example 12 Composition 3 3.92 Example 13 Composition4 3.96 Example 14 Composition 5 3.78 Example 15 Composition 6 3.86Example 16 Composition 7 3.91 Example 17 Composition 8 3.79 Example 18Composition 9 3.80 Example 19 Composition 10 3.75 Example 20 Composition11 3.68 Example 21 Composition 12 3.70 Comparative Comparative 4.42Example 1 composition 1 Reference Reference 4.05 Example 1 composition 2

As is apparent from the above results, a salt and a resist compositionincluding the salt of the present invention exhibit satisfactory lineedge roughness (LER).

INDUSTRIAL APPLICABILITY

A salt and a resist composition including the salt of the presentinvention exhibit satisfactory line edge roughness and are useful forfine processing of semiconductors.

The invention claimed is:
 1. A salt represented by formula (I):

wherein, in formula (I), R¹, R², R³, R⁴ and R⁵ each independentlyrepresent a halogen atom or a perfluoroalkyl group having 1 to 6 carbonatoms, R⁶, R⁷ and R⁸ each independently represent a halogen atom, ahydroxy group, a fluorinated alkyl group having 1 to 6 carbon atoms oran alkyl group having 1 to 12 carbon atoms, and —CH₂— included in thealkyl group may be replaced by —O— or —CO—, m5 represents an integer of1 to 5, and when m5 is 2 or more, a plurality of R⁵ may be the same ordifferent, m6 represents an integer of 0 to 3, and when m6 is 2 or more,a plurality of R⁶ may be the same or different, m7 represents an integerof 0 to 3, and when m7 is 2 or more, a plurality of R⁷ may be the sameor different, m8 represents an integer of 0 to 4, and when m8 is 2 ormore, a plurality of R⁸ may be the same or different, in which1≤m5+m8≤5, and AI⁻ represents an anion represented by formula (I-A):

wherein, in formula (I-A), Q¹ and Q² each independently represent afluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, L¹represents a group represented by any one of formula (b1-2), formula(b1-3) and formula (b1-5) to formula (b1-8), and Y¹ represents a methylgroup which may have a substituent or an alicyclic hydrocarbon grouphaving 3 to 18 carbon atoms which may have a substituent, and —CH₂—included in the alicyclic hydrocarbon group may be replaced by —O—,—SO₂— or —CO—:

wherein, in formula (b1-2), formula (b1-3) and formula (b1-5) to formula(b1-8),* and ** represent a bonding site, and * represents a bondingsite to —Y¹, in formula (b1-2), L^(b4) represents a single bond or adivalent saturated hydrocarbon group having 3 to 22 carbon atoms, L^(b5)represents a single bond or a divalent saturated hydrocarbon grouphaving 1 to 22 carbon atoms, a hydrogen atom included in the saturatedhydrocarbon group may be substituted with a fluorine atom or a hydroxygroup, and —CH₂— included in the saturated hydrocarbon group may bereplaced by —O— or —CO—, and the total number of carbon atoms of L^(b4)and L^(b5) is 22 or less; in formula (b1-3), L^(b6) represents a singlebond or a divalent saturated hydrocarbon group having 1 to 23 carbonatoms, a hydrogen atom included in the saturated hydrocarbon group maybe substituted with a fluorine atom or a hydroxy group, L^(b7)represents a single bond or a divalent saturated hydrocarbon grouphaving 1 to 23 carbon atoms, a hydrogen atom included in the saturatedhydrocarbon group may be substituted with a fluorine atom or a hydroxygroup, and —CH₂— included in the saturated hydrocarbon group may bereplaced by —O— or —CO—, and the total number of carbon atoms of L^(b6)and L^(b7) is 23 or less; in formula (b1-5), L^(b9) represents adivalent saturated hydrocarbon group having 1 to 20 carbon atoms, and—CH₂— included in the divalent saturated hydrocarbon group may bereplaced by —O— or —CO—; L^(b10) represents a single bond or a divalentsaturated hydrocarbon group having 1 to 19 carbon atoms, and a hydrogenatom included in the divalent saturated hydrocarbon group may besubstituted with a fluorine atom or a hydroxy group, and the totalnumber of carbon atoms of L^(b9) and L^(b10) is 20 or less; in formula(b1-6), L^(b11) represents a divalent saturated hydrocarbon group having1 to 21 carbon atoms, L^(b12) represents a single bond or a divalentsaturated hydrocarbon group having 1 to 20 carbon atoms, and a hydrogenatom included in the divalent saturated hydrocarbon group may besubstituted with a fluorine atom or a hydroxy group, and the totalnumber of carbon atoms of L^(b11) and L^(b12) is 21 or less; in formula(b1-7), L^(b13) represents a divalent saturated hydrocarbon group having1 to 19 carbon atoms, L^(b14) represents a single bond or a divalentsaturated hydrocarbon group having 1 to 18 carbon atoms, and —CH₂—included in the divalent saturated hydrocarbon group may be replaced by—O— or —CO—, L^(b15) represents a single bond or a divalent saturatedhydrocarbon group having 1 to 18 carbon atoms, and a hydrogen atomincluded in the divalent saturated hydrocarbon group may be substitutedwith a fluorine atom or a hydroxy group, and the total number of carbonatoms of L^(b13) to L^(b15) is 19 or less; in formula (b1-8), L^(b16)represents a divalent saturated hydrocarbon group having 1 to 18 carbonatoms, and —CH₂— included in the divalent saturated hydrocarbon groupmay be replaced by —O— or —CO—, L^(b17) represents a divalent saturatedhydrocarbon group having 1 to 18 carbon atoms, L^(b18) represents asingle bond or a divalent saturated hydrocarbon group having 1 to 17carbon atoms, and a hydrogen atom included in the divalent saturatedhydrocarbon group may be substituted with a fluorine atom or a hydroxygroup, and the total number of carbon atoms of L^(b16) to L^(b18) is 19or less.
 2. The salt according to claim 1, wherein Y¹ is an alicyclichydrocarbon group having 3 to 18 carbon atoms which may have asubstituent, and —CH₂— included in the alicyclic hydrocarbon group maybe replaced by —O—, —SO₂— or —CO—.
 3. An acid generator comprising thesalt according to claim
 1. 4. A resist composition comprising the acidgenerator according to claim 3 and a resin having an acid-labile group.5. The resist composition according to claim 4, wherein the resin havingan acid-labile group includes at least two of a structural unitrepresented by formula (a1-1) and a structural unit represented byformula (a1-2):

wherein, in formula (a1-1) and formula (a1-2), L^(a1) and L^(a2) eachindependently represent —O— or *—O—(CH₂)_(k1)—CO—O—, k1 represents aninteger of 1 to 7, and * represents a bonding site to —CO—, R^(a4) andR^(a5) each independently represent a hydrogen atom or a methyl group,R^(a6) and R^(a7) each independently represent an alkyl group having 1to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbonatoms, or a group obtained by combining these groups, m1 represents aninteger of 0 to 14, n1 represents an integer of 0 to 10, and n1′represents an integer of 0 to
 3. 6. The resist composition according toclaim 4, further comprising a salt generating an acid having an aciditylower than that of an acid generated from the acid generator.
 7. Amethod for producing a resist pattern, wherein the method comprises: (1)a step of applying the resist composition according to claim 4 on asubstrate, (2) a step of drying the applied composition to form acomposition layer, (3) a step of exposing the composition layer, (4) astep of heating the exposed composition layer, and (5) a step ofdeveloping the heated composition layer.
 8. A salt represented byformula (I):

wherein, in formula (I), R¹, R², R³, R⁴ and R⁵ each independentlyrepresent a halogen atom or a perfluoroalkyl group having 1 to 6 carbonatoms, R⁶, R⁷ and R⁸ each independently represent a halogen atom, ahydroxy group, a fluorinated alkyl group having 1 to 6 carbon atoms oran alkyl group having 1 to 12 carbon atoms, and —CH₂— included in thealkyl group may be replaced by —O— or —CO—, m5 represents an integer of1 to 5, and when m5 is 2 or more, a plurality of R⁵ may be the same ordifferent, m6 represents an integer of 0 to 3, and when m6 is 2 or more,a plurality of R⁶ may be the same or different, m7 represents an integerof 0 to 3, and when m7 is 2 or more, a plurality of R⁷ may be the sameor different, m8 represents an integer of 0 to 4, and when m8 is 2 ormore, a plurality of R⁸ may be the same or different, in which1≤m5+m8≤5, and provided that: at least one of m6 and m7 is an integer of1 to 3, or 2≤m5+m8≤5, and at least one of R¹, R², R³, R⁴ and R⁵represents a chlorine atom, a bromine atom, an iodine atom or aperfluoroalkyl group having 1 to 6 carbon atoms, or at least one of R⁶,R⁷ and R⁸ represents a chlorine atom, a bromine atom, an iodine atom, ahydroxy group, a fluorinated alkyl group having 1 to 6 carbon atoms oran alkyl group having 1 to 12 carbon atoms, and —CH₂— included in thealkyl group may be replaced by —O— or —CO—, and AI⁻ represents an anionrepresented by formula (I-A):

wherein, in formula (I-A), Q¹ and Q² each independently represent afluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, L¹represents a saturated hydrocarbon group having 1 to 24 carbon atoms,and —CH₂— included in the saturated hydrocarbon group may be replaced by—O— or —CO—, and a hydrogen atom included in the saturated hydrocarbongroup may be substituted with a fluorine atom or a hydroxy group,provided that —CH₂— which connects to —C(Q¹)(Q²)- is not replaced by—O—, and Y¹ represents a methyl group which may have a substituent or analicyclic hydrocarbon group having 3 to 18 carbon atoms which may have asubstituent, and —CH₂— included in the alicyclic hydrocarbon group maybe replaced by —O—, —SO₂— or —CO—.
 9. The salt according to claim 8,wherein Y¹ is an alicyclic hydrocarbon group having 3 to 18 carbon atomswhich may have a substituent, and —CH₂— included in the alicyclichydrocarbon group may be replaced by —O—, —SO₂— or —CO—.
 10. An acidgenerator comprising the salt according to claim
 8. 11. A resistcomposition comprising the acid generator according to claim 10 and aresin having an acid-labile group.
 12. The resist composition accordingto claim 11, further comprising a salt generating an acid having anacidity lower than that of an acid generated from the acid generator.13. A method for producing a resist pattern, wherein the methodcomprises: (1) a step of applying the resist composition according toclaim 11 on a substrate, (2) a step of drying the applied composition toform a composition layer, (3) a step of exposing the composition layer,(4) a step of heating the exposed composition layer, and (5) a step ofdeveloping the heated composition layer.
 14. The resist compositionaccording to claim 11, wherein the resin having an acid-labile groupincludes at least two of a structural unit represented by formula (a1-1)and a structural unit represented by formula (a1-2):

wherein, in formula (a1-1) and formula (a1-2), L^(a1) and L^(a2) eachindependently represent —O— or *—O—(CH₂)_(k1)—CO—O—, k1 represents aninteger of 1 to 7, and * represents a bonding site to —CO—, R^(a4) andR^(a5) each independently represent a hydrogen atom or a methyl group,R^(a6) and R^(a7) each independently represent an alkyl group having 1to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbonatoms, or a group obtained by combining these groups, m1 represents aninteger of 0 to 14, n1 represents an integer of 0 to 10, and n1′represents an integer of 0 to 3.